I've only played Indy about 3 maybe 4 times in person.
The big issue is the path of adventure. If that is working the game is better, but at least 1 of the times I was playing it wasn't working. Even working its still not the best mech.

But, MM castle is one of the best all time mechs/toys in pinball. Just amazing. I like rules. I like the lock shot.
And I think it has nice energy and great callouts and a nice sense of humor. Because each castle lord has a unique personality that helps break up the tedium or monotony of doing the same thing over and over. As you get new callouts for each sequence.

I hope to own both games someday. But, for me. MM I like just a little bit more.

I think grind is fair for MM. It is a grind and it has a lot of wood chopping. But, I also like the strats that you can employ.
I do prefer AFM over MM as well. I think AFM has more variety in the strats and flexibility if you miss or mess up your strategy. I also like the sci fi theme better.