@PLAYING TO WIN
Before anything, I am NOT good at Injustice 2, I just enjoy the crap out of it.
So, as an older gamer, particularly from the SF2 and MK arcade days, we were always learning every character. None of those games have particularly heavy execution, yet the SF2 series in particular still has incredible depth and tech is still being found to this day.
I completely enjoy being able to put in some time learning characters and getting more from my game than just labbing and grinding one single character for years and years. It is very enjoyable to me to see games being made where the barrier of execution is just high enough that you can't just mash and watch combos happen, but you have to be competent with specials, and at least have a game plan regardless of what character you're using and who you're fighting against. This allows me to begin learning more than just a single character for years. Instead, I can spend a couple weeks and move to the next, giving me vital information on each character, and potentially learn strategies to beat them.
I don't think it's bad AT ALL to see more players learning more characters. I think it makes it exciting to see when a player who is known for using or maining a single character suddenly whips out 3 or 4 different characters in a tournament because they can.
While you can say that having to spend years to learn a single character increases longevity, the opposite argument could be made as well. Being forced to stick to your main because you've committed so much time can get boring and cause you to drop a game. In that light, being able to relatively easily pick up and begin learning, at a competent level, multiple characters, can also increase the longevity and excitement of a game.