The skill difference between Masters and GM is pretty big (not talking about peak 4k people - people who are 4,2k+ and are able to stay there and climb)
The only thing that hasn't improved that much is aim (even that depends from person to person).
Getting mid/high GM is about knowing your positioning, being able to time your skills right, better ult management, giving IMPORTANT information to your team (when they're in voice - even in GM people don't give a flying fuck) and ofc keep working on your aim, even if the difference is not that big.
There are a lot one tricks in GM, so "don't be a one trick" is bullshit. It's just easier most of the time when you aren't, except when you perform godly on your hero.
It's about self-improvement to get there, but kinda about luck and other things how fast you will get there.
Btw peaking 4k is easy, climbing and maintaining is the harder part