Which is more profitable – an MMO with a monthly subscription or a free-to-play game?

Sometimes, while just passing by/swimming/flying, I would observe bots, but very rarely, and I have strong doubts that this method can generate a large income of in-game currency. Have you tried this method? Or maybe there have been cases where someone got excellent gear just thanks to this?

I acquired a mount pet, a decent flying mount, and some gold gear using bots. Of course, it's far from the level of donations. But based on my experience, I can say this: if you want to play without investing anything, you'll have to run bots for 3 months (or even a year), and not just in one window. It's possible, but it's a long process.
Right now, I'm saving up for a better flying mount, and looking at the exchange rate, it seems quite realistic.