No it shouldn't.
If you want a solo mode for solos that's designed for solos. Then get Bunge to add Rumble as a sub mode in Trials. If you're against that then you're evidently not thinking about solos properly.
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You're not really changing the game mechanics by doing rumble either it just becomes a FFA instead. But if we're going to divide the playlist at least do it right. You know people still -blam!- when it was Freelance right? They complained about the MM (which was valid) but they'd moved from one excuse to another.