Here's the meta breakdown from the first challenge after the restriction of Gush:
You can see that the numbers of metagamePostGush are very similar to what we have now in metagamePostMentor, except that metagamePostGush is actually much more diverse (more combo, more Oath, etc.)
The metagamePostMentor data, which is less diverse, suggest that the metagame will become quickly consolidated and even less diverse as people are able to netdeck more. (assuming that the metagame will behave in a similar trend, which have no reason to assume otherwise)
The given is that the metagame will "tighten up" and become less diverse since the evidence over the last 6 months suggests that netdecking is the most prominent form of deck construction. Since we are already at a less diverse starting point, the new metagame will undoubtedly be less diverse than the previous metagame (before the restriction of Mentor).