As far as your Sadira fight.
Also, I don’t know how familiar you are with some terminology, so I will be adding some explanations in case you’ve never heard of some of this stuff.
First, you’re staying in range of Sadira’s lights which are very fast startup and will likely beat any normal Thunder throws out at point blank. They are fast, but low priority. The Sadira player also was mashing a bit from my perspective, you need to turn that against them. The way you do it is you make him afraid to hit buttons on wakeup (the moment as he gets up off a hard knockdown). Thunder has a lot of ways to do this, as his archetype gives him the advantage of being an intimidating bully at that range.
I would recommend staying close to them but just outside Sadira’s lp and lk ranges, and use either a MP or HP to counter. You are just outside her reach, but with him mashing on wakeup, the opponent doesn’t care, and Thunder’s long reaching MP, HP, MK, and HK all can punish those mash tendencies if correctly spaced. Practice it in training, and you’ll see what I mean. Also, meaties work wonders and Thunder has some good ones, use them.
Meaties are moves that have lots of active frames for the duration of the attack. An example is his crouching HK, which is Thunder’s sweep. Timed correctly as they are getting up, Sadira either has to block it, or use a move with invincibility to escape it, and without meter her options are limited mostly to blocking it. If they try anything other than a block, or an invincible reversal (which I think Sadira’s only one costs meter), they get hit by the sweep, and that sweep hurts when it registers as a counterhit. If he feels like mashing, meaty sweep, meaty HP or HK, meaty Triplax. Takes a little practice on the timing, but you can get it without too much trouble after just a tad of timing practice.
Your use of the Shadow Grab is good, but not perfect. I like that you recognize good key moments to use it, but your follow up to it needs work. Against Sadira, you hit with his MK, which is good, but cancelled into ankle slicer, which you should replace with Sammamish (his DP). His DP will keep them juggled, and using his Skyfall follow up causes a ground bounce on the opponent allowing you to follow up with another normal into ANOTHER DP, which gives rise to his DP bounce combos. Finally, if you manage to keep them juggled long enough, and you have another meter, finish the combo with Shadow DP, and cash out that damage!
I know that last one has some advanced juggle combos in it, so that will take a good bit of practice, so start small and try to do a Shadow Grab and hit them with his MK and cancel into his DP, then after getting that, just add the HK button to do the skyfall add on.
At the mid round, you ended with a Wall Splat ender. Since she was low on health already, I would have probably ended the round with the Ankle Slicer ender and tried to earn some meter for the next round, especially since you used one meter to do a Shadow Triplax linker. Always look for ways and moments to build your meter, as Thunder is always more dangerous with it.
When you jump in at an opponent, a good move to use is the jumping HP, but when jumping over them, use jumping MK instead. J.MK is Thunder’s cross up move, which has a large hitbox, and lots of active frames, and used correctly, is hard to block because it can sort of hit behind him (a property of cross moves). When used at certain distances and timing, the opponent has to guess the correct way to block, and when they guess wrong, free combo for you. Go to training, and turn on hitboxes and do a j.MK and see the hitbox for yourself. It’s a neat tool.
Thunder has good jumping normals, but his best work is done from the ground, try to not jump around a bunch.
For the Riptor fights.
Keeping your eye on both the combo and the KV meter is something you’ll need to work on, but know that the light the linkers and doubles you use, the quicker you should end your combo because they fill up the KV meter the fastest. I would recommend using the audio tool that has a hard bass note that increases in volume as the KV meter approaches full, as a training tip to start you out.
Always end any combo off a back throw quickly, or use your instinct to reset the KV to zero and chance getting a higher damage combo. Usually good for either putting your opponent into the wall for a wall splat or building up some meter with a meter ender.
If Riptor likes using his fire attack a lot, wait until the third hit and punish appropriately, or if you have meter, use Shadow Triplax. Shadow Triplax has armor, meaning it can absorb one hit and keep on going, in which it will absorb Riptors fire, and before Riptors second blast of firebreath is out, you’ve hit him with a triplax opener. If nothing else, DP him, because all versions of Thunder’s DP have projectile invincibility, but even if you miss Riptor and go over him, you can follow up with Skyfall for a hard to react cross-up.
Save Shadow Grab for when you are sure you can punish him. That’s one stock of meter that you should use carefully, and missing a Shadow grab is hard punishment. Don’t throw it out too wildly, as there was one moment where you threw it out against Riptor when he was airborne.
You used the launcher ender once, and I’m not sure if it was an accident. If it was, work on making your inputs a little more fluid and precise. We all slip up on our inputs once in a while though, so don’t take that too hard. If you do get a launcher ender though, try some DP bouncing combos as a follow up, or get a Call of Sky charge in for a free crows dash.
That Riptor player is not using Riptor’s anti air moves correctly. He also liked to guess break at the very first moment he could a lot of the time, so a counter breaker after an opener isn’t the worst guess in the world, and would actually be a decent gamble. Just be observant and try to notice patterns like that if you can. Talks a little practice like all things.
Overall, I’d say you need to try learning the reach of Thunder’s normals, and recognized that he has long reach for a reason. When they won’t let you close, you have to put in some reach. A lot of Thunder’s moves have forward momentum, and benefit him in a such a manner as to get him in on the opponent more easily.
Be careful not to go airborne too much, Thunder’s jump is sort of…floaty compared to most others in the game, and he’s slightly easier to anti air for it. If you do jump in, I would recommend using j. HK from really long ranged jump ins, j.HP for mid screen jump ins, and if you’re close, a j.MK crossup will sometimes net you some good damage opportunities.
You need to try and work in your regular grab into your game plan, not just the shadow version. The regular grab has awesome damage too, and can be cancelled off of normals. However, if they are in block stun, it will whiff and leave you vulnerable, and if they are in hit stun, it will count as opener ender and be breakable. Trying using something like cancelling a MK into a heavy command grab. It’s a deceptive tool, and they’ll be too programming to try and block it to even think they have to jump to avoid it.
Finally, you seem to be making good use of your tools available, but you’re unaware of their full potential, and you leave damage on the table sometimes because you don’t know that one move is better to use than another, or has a unique property like lower body invulnerable, projectile invulnerable, armor, etc.
You’re on your way, don’t get discouraged. We’ve all started from zero at some point, and to get better, the first step of improving, is recognizing you want and need to improve, then finding ways of doing so.
Also, sorry for the wall of text. Hopefully there is something in this wall that can help you. Best of luck.