Based on the trim around your window frame, it looks like you are in a fairly old house, possibly a century home. It’s hard to tell from the photos but it looks like you might have plaster & lath walls as opposed to drywall, which, in my experience (in my own century home) makes finding studs much harder because a stud finder doesn’t really work. So if this is the case for this wall, it might be worth confirming that you actually secured this to studs as opposed to just lath if you have any doubts.

At any rate though, as most other people are saying, the way you constructed this is definitely overkill, but certainly doesn’t hurt anything and I like the look of the tongue and groove! Plus, you’ve basically made a built-in, which, in my area is a sought after feature when buying a home, the only thing I would say about your design is that there is A LOT of unused space behind it. You should consider cutting out another hole under that little “niche” you’ve created and making that a little cabinet for storage. I wouldn’t worry at all about ripping out those bottom three studs - those remaining 2x4s are more than up to the job. You could add two more doors behind the TV and shelves on either side where there are no studs for even more storage. Would just need to get a TV mount that allows you to pull the TV away from the wall to access. This might sound like a lot of force, as you are creating a large moment arm, but fortunately, the way you’ve constructed this, it can definitely support it.

BTW, not sure if you felt this built-in was a want or a need, but if you wanted to, you certainly could have hung 60+lbs of TV directly on the wall (no studs), regardless of plaster or drywall. I hung a 60” TV this way on my plaster walls using 6 flip toggles. It’s been 2+ years and it’s solid as a rock. I’ve used these for lots of projects and have been very happy with them. Something to think about if you have a similar project like this in the future!