Many such MMOs exist or have existed without character levels. It's not a new concept.The mmo that throws that mould away will be interesting to watch.
Linearity is highly comforting to humans so long as it doesn't become constricting.
A tutorial concedes poor game design. Having more tutorials doesn't alleviate the poor design of MMOs.One thing I think MMOs could make use of pretty well is something I saw LoL do. There's sort of a tutorial but before you start it you answer a question or two about your experience with RTS and MOBAs, then depending on how you answer you are put in different tutorial modes before really playing.
And one you likely believe it out of familiarity, ubiquity and mass market expectation. That is a non remedy.
The problem that is systemic to MMOs is that they only exist as vehicle for social play. No gameplay function is better served by the genre otherwise. This creates an issue whereby design must deliver a set of demonstrable rules to desperate persons able to interact with each other in ways not totally controlled by the developer/designer.
The problem is presenting transparency of game mechanics in a game space that has to be shared to achieve it's goals. Depending on the sub genre of MMO, this can be done to varying degrees of success. However, as I pointed out above MMORPGs have historically not been able to deliver their game mechanics in a compact and transparent method without arbitration.
World of Warcraft does it the best as far as I know. By level 10-ish almost all core systems and motivations of the rule set are revealed. It's still one of Blizzard's greatest masterstrokes of design; Ellowyn Forest.
But I am keen to point out "almost" and "core" in the above. Because it's still not compact or dynamic enough to deal with the impression of other people sharing a limited game space in real time, persistently.
It might not be a solvable problem, in truth. In the same way an FPS can not reasonably solve platforming mechanisms without creating specific devices to allow the presence of platforming to make consistent, logical sense in the context of an FPS. Portal 2 does this to the greatest effect we have ever seen- a lengthy lecture was held on this fact some years ago.
Anywho, yea. MMOs are not particularly good games.