For the whole "It must have took this guy over 140 hours!" is rather incorrect, you only need to complete 7 secret levels (7 different gems, each set of levels have their own gems) you can also do it with any team in order, so for the easiest and fastest way to get through those secret levels if you're not good at the game is to run through team rose and collect those damn chaos emeralds, after that your last goal is to complete the game four times separately wtih each team. Most of that time is probably spent off getting mulitple A ranks by trying not to die, collecting rings, not going too slow, etc. At worst it's roughly ~10 to ~20 hours to complete it.
Team Chaotix is not just 'collect seashells: the game', but they are what they are, a gimmicky mission mode variant of the normal stages, this is just the fault of skipping 75% of the game as Ross did in the video and probably just overlooking the actual checklist to unlock the final extra special stage, since he mentioned ShadOW THE hEDGEhog that does it slightly more worse for trying to unlock the final extra special secret sauce stage with having to complete the game roughly ten times in a row (there's some extra caveats as well on that as well but knowing Ross he might blow it up more than he should if by going Sonic Heroes)
Light Dashing rings that are in mid-air especially for that castle section are best done jumping towards it and light dashing rather than walking off and hoping for the best.
The homing jump isn't the most automatic/braindead thing ever, since you were pressing less than ~2/5 of a second (going off by frame counting of 12/13f of a 30fps video), you have to be more accurately with your movement in the air with the left stick and actually have face towards the enemies, turn in mid-air and doing it fast & correctly, luckily all of the characters have a jump arc that stalls throughout their jump including the apex for a rather lengthy amount of time, so you just needed to press & aim slower rather than just pressing it fast.
That last section in the last level with all the lasers, have to break it to you Ross but you just went too slow with knuckles instead of using sonic because of your previous trauma/behavior, see this longplay at ~1:43:25 for example
I could probably explain why in the second level with the automatic loopdeloops if I had better memory, but the reason why you're not exiting with enough velocity is if I recall it's how you mess with the left stick not only entering that section, but also during & exiting it, just by using game footage to look back on you can't really tell without extra stuff like recording your inputs as well and being experimental.
Sonic's age is stated to be 15 while Amy was either 8 or 12, so your theory is kind of correct
It's kind of weird seeing Ross thinking Sonic just go fast the game when he ultimately explained it perfectly with Sonic 1 (although later 2d sonic games did it better with sonic 2, 3&K, etc.), there's nothing wrong with going slow when going fast, it's part of the nature of going fast, it's easy to go fast on a very flat straight line, it's multitudes harder to go fast when there's 5 consecutive hairpins, the difficulty of clearing obstacles that force you to go slow, fast is part of the challenge of going fast.