It could be as you say, but what exactly are the perks of staying mp4 and not rushing to mp5?
I remember, when finally deciding to advance from mp3 4-5 years ago, I, too, wanted to explore more of what mp4 offers. And there were only a few mp4s, so I asked Tal, after one or two months, to cap me. I wanted a 'steady' progression, but I found mp4 wasn't offering much, perhaps due to the lack of people at that mindpower.
For mp3, if I remember correctly, fighting is very easy, and you can enjoy pummeling with some vicious ritual with (tokened) imps, jokers, pimps etc It's a 'carefree state', although you're not capable of doing much (or as much). That's a perk in itself.
For mp4, it's only interesting as long as you have companions, isn't it? Perhaps I'm not aware of some options?