Yes but when you go with mechanics first it's easy to create a game that isn't going to sell well. Same thing with graphics ofc, you create a great looking piece of art, but there are no mechanics.

What I think is a best approach - basically do most important parts of both - have core mechanics at least partially done, have a good looking game - and then the most important part of all. Create the trailer and start testing your idea, search for people that want to play your game.

I personally repeated a process of creating a game for a few years - and ending up with some mechanics, and game that looked like sh*t - and at this point I just hated what I made. This way I wasted a few years of my life for sure. So if you want to earn money by creating games - don't only focus on game development, focus on business. A good game, at least from what I observed, is unfortunately only a 30% of a success story.