Only-XL - I wouldn't recommend it; in my opinion, it's the most boring thing in Heroes.
Diamond - it exists, although this year it's in an experimental format; we'll see how it goes.
By the way, I agree with you about OnlyXL, but public opinion says otherwise. That's why 6lm10a is currently the most popular template.
And there are specialized tournaments for different Castles. I don't really understand why there's so much criticism of the ramp-up tournament; you yourselves complain from time to time that the developers don't always listen to player feedback. In this tournament, the developers decided to listen - they offered one of the options for changing diplomacy, which could be implemented in HotA, so that players could try it out and express their informed opinion. In my opinion, the result has been more than achieved.
Excellent Company, 3 in 1, 9 Kingdoms, Path to Olympus, Charity - they are all roughly similar to OFB-FB, because they are played with a wide pool of templates according to standard rules. Maybe there just aren't enough of these types of tournaments?