For me, him not struggling doesn't automatically mean he's already around YC level or so. The way I see it, Zoro was either equal to Luffy or a step below, at all times until Whole Cake. There we saw where Luffy was in relation to the big dogs and improve by leaps and bounds by the end.
Zoro hasn't shown any hint of that and no amount of training will make me believe he's there. While he hasn't shown everything he can do, he hasn't gone through anything like Luffy did, so for him to, somehow, be on that level already is a step to far for me.
Again, that's not to say he's weak. I straight up said he's a top 5 combatant in this war and an invaluable asset, I just don't think he's the 2nd strongest at this point. Like Luffy in Whole Cake, I expect him improve during whatever major fight he has in Wano. Then, I'll happily say he's YC or whatever.
Until then, Shutenmaru is my choice still.