I watched the first video and assume the OP was the guy in red. Had a hard time determining who was 3.5 and who was 4.0 in that video. They both looked very 3.5ish, i.e. lots of UE's, very little consistency and not much in the way of weaponry other than fitness.
I think there is good recovery footwork but poor setup footwork (lots of reaching). I think the strokes were often too delicate and deliberate and not loose and free swinging, leading to very few balls going deep. A lot of the rallies were played inside the baseline.
Too much arming. Too many DF's especially given the serve speed wasn't terribly fast.
Sometimes I think fear of losing inhibits people too much in their development. Throw that fear away and focus on the process of becoming a good tennis player. Hit out with power, even if you send some long. Think of the fundamentals - unit turn, knees bent, low to high, hit off the front foot, head still. Pick one to work on every day and focus on that fundamental. Don't worry about the outcome. As you improve, winning will happen as a byproduct of committing to the process of developing a good foundational game of tennis.
Personally, I would suggest one thing and that is work on your lower body which includes speed, movement, position, and hustling. If you improve in that you can have more time to set up nice strokes and that is actually the second thing I recommend is develop cleaner strokes and pay attention to your grips. Also concentrate intently on your shot and slow things down with your mind, you have more time than you think, don't rush. Lots of silly mistakes can be avoided for sure.
@NuBas & @S&V-not_dead_yet I appreciate the feedback! I definitely need to loosen up on my game to become more fluid while also focusing on core fundamentals. Definitely will be taking more risks with more angled shots and shot selection in general.
Wow just like your groundstrokes you need to be more fluid and relaxed on your serve. To do this you need to coordinate your toss and work on a fluid loop on your serve as well. Essentially at the same time you start your drop you want to be turning your shoulders. If you toss at the right time you will come up out of your drop and contact the ball at the right height.
The trick really is coordinating these three variables. Teaching pros will have students shadow swing to get the feel for this..
Quite a few videos on this by teaching pros if you have time to look it up.. Main thing is to really understand what is going on.
People often focus on relaxation - but if you just allow the racquet to loop down and don't have the timing on the toss right - this is not going to work (obviously).
You should be coming up under and on the left side and then finishing "over" the ball to the right. Instead this basically looks like a flat serve. This from what I could tell is mostly because of the racquet position before extension - it's behind you coming pretty much straight forward to the ball instead of behind your back coming up to the ball.
I'd say besides consistency, which others mentioned (at 4.0 you should be able to hit rally balls pretty much all day without error), I'd work on serve - especially second serve. Develop a spin - yours are basically slightly softer versions of your first serve and red meat to a decent returner. Spend whatever time is necessary to develop a true spin serve first, then modify it for a kick serve.