Very wonderful point raised!
First of all I would like to anwer the second question cause its short answer
- YES! If you see an average 1000 rated player from 2015 he would surely be weaker than a 2022 1000 rated player. Youtube, twitch has provided immense learning material. And pandemic too has played a role for the emergence of new chess players, the youtubers have made chess a thing that common person can follow and understand better than ever before.
- Openings or Midgame? I would say openings are important to learn cause if you dont, you simply be dominated by opponent cause you dont know what plan to follow, its not necessary to go in depth but a little knowledge of opening provides easy and smoother play. Chess has become, to a bit extent a memory game too, unfortunately.
- You can work on midgame and tactics by puzzles and watching games of Grandmasters but opening is what you have to do on your own depening on your ay style.
I Hope i covered it all. 
I started playing chess about a year ago, but really only played for a few months. I've spent the vast majority of my time playing against the engine/(computer) to learn how to play, as it gives me the ability to multitask, minimize the window and return to the game later. So far I've been able to consistently beat the 1100-1200 engine, as well as the NPC character modeled engine players (up to Nelson).
It appears the character modeled computer players were programmed to play chess a certain way.
1. Is it better to just play against the engine so that I'm not constantly seeing the same exact opening from the appropriate level character modeled player? Or is the engine itself similar, in that if you choose 1200elo engine, it will play the same way more or less? I ask this because some of these character modeled players do the exact same opening every time, and I find that they're incredibly easy to beat once you know how to exploit them. Is the regular engine the same way?
2. Is it better to learn how to play chess against human players?
Theory/tactics/endgame questions
I continue to hear from chess players the following sentence "learning openings (theory) is not as important as learning middlegame/endgame". I'm assuming they're referring to tactics and checkmate patterns. I don't disagree. Yet, this doesn't appear to be what I experience with chess players. Players at the 1000-1200 range are almost all using some amount of theory, because they know openings.
1. Should I spend more, or even most of my time learning tactics and checkmate patterns, instead of learning how to defend against/learn certain openings?
2. Has the game changed over the past 5-10 years because of YTube and websites like this one, where lower level players are more versed in theory than ever before?