My issue with layer 2 systems is that there generally doesn't seem to be a clear consensus or schelling point/mechanism for how to proceed when there is a breakdown in consensus.

In Bitcoin and most PoW crypto networks the 'longest PoW' is a widely agreed upon metric for what gets to be called 'Bitcoin' and what needs to find its own brand after a split. In Steem, DPoS, there are voting mechanism which decide what is the 'valid' continuity when there is a split. Even when Hive was more popular than the "original" Steem, the chain which the top witnesses decided to continue with, still got to continue as "Steem".

On the other hand with Layer 2 systems, we don't have clear mechanisms for what is valid when the rules need to change or there is a major split in the community. You used Omni as an example, in November 2017 Omni released a 'mandatory fork'. There was no consensus mechanism, all users had to change their software or it would not be valid for Tether. They had the power to do this because if Tether only respects a particular version, then everyone else doesn't really have an option (they will not redeem tokens on other versions). Other 2nd layer systems have similar dynamics - if an online card game changes the software that decides which card tokens are valid, most likely you will have no option but to go along with their change. Even if the change is unpopular, there is no clear way to determine what is the 'valid' continuity beyond "it's this version because we say it is".

Layer 2 systems could establish some set of rules ahead of time for deciding valid continuity, but I have not seen clear examples of this being done and followed through with, and establishing consensus is not really a core part of layer 2 projects in general, layer 1 projects tend to have such by default.

I recognize that this doesn't decide what is valid or more valuable, people and particularly exchanges do. But it does help people quickly decide valid continuity without defaulting to the developers having special authority each time.