I'm not going to pretend to know the history of your formats, nor do I have a strong opinion about which specific format should be chosen for this tournament, but I do want to take a moment to make a case for Monothreat to be included. I played Monothreat in MWP this season and I've genuinely rarely enjoyed playing in a side tournament as much as this one. For those of you that know me a little, I play in a LOT of tournaments like MWP in all kinds of different tiers and formats, so that does actually hold a little bit of weight.
First of all, the emphasis on team building that people have outlined as a concern for Monothreat actually goes the other way, too. I came into MWP having never even heard of Monothreat and I built all of my teams throughout the tournament myself. There is no metagame knowledge you have to catch up on, there are no commonly used sets you have to get used to and you don't need any big team building support either. You get assigned a type, you look at what you think is good and you prepare for each metagame as well as you can as it comes. That's it. I've loved seeing how every Monothreat player approached each typing differently as well. I didn't run into mirror matchups at all throughout MWP and always found myself using different Pokemon and movesets than my opponents were using. Any region, no matter how many established Monotype players they can field, can get a competitive Monothreat slot going.
As for the competitiveness, I'd argue that Monothreat is particularly competitive as you can't run into a nightmare matchup you didn't foresee or weren't able to cover in the team builder. You know what's coming, so if you get caught out it's simply on you. My team lost the MWP final this weekend and we, bluntly put, got absolutely eviscerated by the Centiskorchers (congratulations btw, you guys were clearly the better team) in the regular Monotype slots after running into awful matchups game after game. We won our Monothreat game, however, and just like in semis my managers would've picked me to play Monothreat in the tie breaker if it needed to come to that, simply because it was more reliable and more in our team's control to win a game that way. How is that not competitive?
Finally, I want to touch on type overlap, because that's actually big when this tournament follows up MWP relatively soon. If Monothreat is selected for this tournament, then we shouldn't repeat types that we've seen in MWP, as teams realistically will just reuse teams from there. Types used in playoffs could be picked, since only two teams were preparing for those, if necessary. I talked to Ticken about this yesterday and even without reevaluating the currently blacklisted tiers, a concept I don't love, we should be able to cover at least the regular season reliably without overlap. I also think that if, to use Fighting as an example, Hawlucha invalidates using an entire typing simply because it's next to unstoppable, that we could consider banning the Pokemon instead of blacklisting the tier entirely. I know part of the ideology is following Monotype's official banlist in Monothreat, but if it's the difference between Monothreat being included or excluded, then surely it's worth thinking about. In any case, we could ensure types chosen in MWP aren't repeated here nonetheless.