An OM may be more feasible as it requires less to maintain, but an official splinter tier is out of the question as far as I know
That's actually a very good point.
UU OMs have worked in the past, and by extension lower tiers are possible as well. I do not have a single doubt that it would work pretty well as one.
However, OMs and their extremely small but effective councils and playerbases also show how ridiculously easy it is to manage a meta,
as well as the ABUNDANCE of tiering respondent. Small playerbases are already perfectly sufficient and effective. In other words, I'll talk as casually as you do, it completely dabs on your "but muh playerbase" speech.
Not to mention that in terms of sustainance, it makes way more sense for a terastal ladder to gain a following considering this is what game players will automatically direct themselves towards, by extension making much quieter a non-tera ladder.
I'm also gonna bring it up again since the question got avoided, ever since bot usage like Scrappie's .alts command got restricted to %driver users and above (I'm not exactly sure when, but I definitely remember when it wasn't like that), the current ladder has had a problem of favoritism, unfairness, and uncompetitiveness. That, once again, terastal largely mitigates.
In other words, terastal is the better ladder in the current state of things.
But "mitigating" and "fixing" are two different things. I normally should not even have to consider a terastal meta, which also suffers to an extent from the problem of scouting, to deal with what is essentially a Showdown problem rather than something coming from Smogon.
I recognize how paradoxal is my position, but NOTHING bot-related was fixed over the past few years since the ban of that-one-mechanic that also mitigated the unfairness issue, so why would we put any faith on Showdown's incompetent side of dealing with the problem?
We wouldn't. Only Smogon can fix it at this point. And clearly, if we must have two main ladders to deal with a problem of uncompetitiveness and favoritism, then it's a price Smogon is willing to and naturally
has to pay.
Which is why it is out of question to not keep a terastal ladder, because with it things are still better.