My take on this is DPP > SS2 > SV4 > UU. I think that we should be looking at this from a perspective of how easy it would be to field a competitive set of players and look at metrics for managers to see what players are good instead of trying to bash each metagame. I feel that everyone is likely to have much more differing opinions about the state of each metagame, and trying to bash metagames seems somewhat unproductive. Of course I actually play DPP, so take whatever I say with a grain of salt here cause there's going to be some pro-DPP bias here.
DPP is in a pretty decent spot right now. I think that DPP got a pretty good boost in OGPL, with newer players like Nuxl, dreepy, and Slip doing pretty well in the tier. I think that DPP should get enough players between Euphonos, stravench, Jamez, Rei, PA, Nuxl, and dreepy. There's definitely other players, like Elo Bandit, Slip, and I who could definitely play DPP if needed, even though we're likely better in other tiers. Anyways, the playerbase for tiers like BW and ORAS is similarly dire, and I think that non-SS old gens having this sort of issue while trying to field a single slot in PL is not a completely new thing.
SS2 seems incredibly close to DPP to me, but I'm only putting it slightly behind. I think that like DPP, it's incredibly possible to field a good set of players here. The reason I have it behind DPP is that I think OGPL showed one of the bigger issue with the SS2 slot, which is that there's a lot less experience in potential SS2 players than DPP players. I also think that the addition of three SV slots would affect the SS2 player pool more than the DPP player pool, which is why I think it's a slightly worse option.
SV4 is where I think we have a pretty massive drop-off here. I do not think that we have the SV playerbase to support a fourth SV slot, and think that World Cup VII showed us a good example of this. Of course, PL is a totally different beast, but the fact is that SV4 dilutes an already somewhat underwhelming SV3 pool. I think it's definitely a weaker option than DPP and SS2, but I think that it's at least been tested, making it better than UU, given that managers would at least have some sort of data to go off of when trying to figure out who to select for a potential SV4 slot.
UU is the worst option to me at this moment but I can definitely see having a UU slot in future tournaments. There has been zero tournament representation so far for UU, with UU's first tournament currently being in signups. The biggest issue with this will be the sheer lack of data that managers will have to go off of in order to make draft plans in SV UU. It might be very possible to find a playerbase for UU, but in almost every case, the players would be better in another slot. I can see UU getting a slot in something like World Cup if it develops well from here, but I think that it is not ready for PL representation yet due to overall just being too new.