i actually share the same sentiment, although for different reasons
zoro not being involved in the fight against the yonko is not a downplay, because it's a fight for the pirate king seat, the supernova captains are the one who should defeat the yonko, the rest of the crew are limited to providing support, it's a completely different playfield compared to zoro ambition to be the WSS, so at the end of the day it doesn't harm zoro's portrayal.
but when it comes to zoro in particular, oda didn't even try to cover up the PIS.
1-zoro didn't use CoA to guard himself from straw man's nails attack
2-zoro didn't use CoC to guard himself from killer's stab
3-zoro getting lost before kaido's appearance
4-zoro getting lost before yamato's appearance
5-zoro being confirmed a conqueror too late in the story
6-zoro not fighting any famous swordsmen throughout the new world
7-zoro failing to cut king, even though he can cut kaido <= this is obviously BS
...