I think it is more that they are becoming the same, somebody finds a niche and gains sub and likes and smaller YouTubers (and others) see this and try and copy it.
I give my subs a clear out once a year or so, I think the best thing is to keep the number as small as you can, I watch a lot of car YouTubers for example:
Shmee150
MrJWW
Salomondrin
Misha Charoudin
Supercars of London
Seen Through Glass
Sophia Calate
Harry's Garage
Jay Leno
one or two others but those above all know each other (not Harry and Jay) and do collaborations every now and then, and 90% of the time they are all doing something different, this weekend it was the Goodwood Festival of Speed and five of them were there, there was some overlap but they mostly did videos of different things, and as they all know each other they I assume know that they have to do their own thing and make their content different even if they are making a video about the same thing.
I agree that in gaming it is a little different and harder to do, there are only a few actual people in gaming that I watch, some specific ones like Don Joewon Song for Forza and BattlefrontUpdates for StarWars and others for other games, then of course Digital Foundry and The Know, but for gaming personality's I only watch a couple, HappyConsoleGamer, Kaceytron and I know he is not welcome here boogie2988 (who I have been going off the last couple of months) but was one of the first I watched, I have just discovered Last Gamer though.
I just think that if you find a few YouTube channels in a genre and make sure they are all different, giving different views, opinions and style that you get a better all round view and also you are better informed and also entertained.
I think that the best Youtubers just keep evolving and they have to so they stay relevant thus gain subs, views and likes and this give an incentive to keep going, I would think that creating content and posting it and it only gets few views is incredibly disheartening.
What's It Like Being A YouTuber? via MrJWW, I don't know if what they say in this video is true, but they are all successful YouTubers so I think it must be true.
EASY STEPS for you to get YOUR DREAM JOB! via Salomondrin a self made millionaire.(there is adult language in this video). don't listen to friends that say 'it will be too hard, you won't make it' instead listen to the people that have made it! and honestly I need to listen myself more to the latter than the former.