You are asking in the wrong sub. This sub is full of bitter people that despise mobile, since it pulls away developers that would otherwise work on PC titles instead. Naturally they will tell you to work on PC.

But do you want an honest opinion? Mobile is where the money is. It's low effort + high monetization that makes it so much more attractive for developers than PC. So that's where you should focus on.

Don't think of a platform as 'dying' or 'thriving'. If you want to be successful as a self-made, always think of the money. That is a lesson everyone learns sooner or later. You just can't make things work without it. No amount of wishful thinking can compensate the lack of money. Even your Magnum Opus will not attract payers if it is on the wrong platform. That is the reality these days. Ask anybody in the industry (except HR guys maybe) and they will tell you the same, UNLESS you wanna go the Early Access / half-baked product bullsh*t route where you perpetually develop and never finish. Developing PC titles these days is just too costly and suck the funds dry before your game launches, on top of that player acquisition and churn rate is rather poor compared to mobile so you can fall on your face really fast after release. The mobile market has faster cycles but is far less risky, you have a huge audience to work with and you don't even need to do great do turn a profit. And by the way, investors know this and they are unlikely to provide you with funds if you made clear you want to settle for PC only.

Just out of curiosity, by MMO veteran do you mean that you have some sort of work experience? If you refer to playing...well I suggest that you get some experience in the industry first so you can get a grip on what works and what doesn't. No gamer turns into an industry professional overnight just by saying so.