so that's your point of view.
Brook faced Big Mom and actually did super well,
Chopper stalled Big Mom for a short moment,
Jimbei faced a mad big mom and stalled her decently,
Marco faced Big Mom, she grabbed him but she wanted pero to kill him but when he failed, she ran away from marco,
The same Marco faced many admirals, two DF BB and he is still fine,
Zoro never got a 1 vs 1 against big mom. The only time Zoro got a 1 vs 1 against Kaido, it was at the end with a broken body that he could avoided easily but unfortunately he took all the damages to save his comrades. How it's fair to say zoro can't if he was healthy ?
The only time Zoro faced Kaido in 1 vs 1 being fine, it was for Hiryu Kaen but it's the only attack Oda wanted to miss when kaido literally tanked +30 or 40 named attacks. That's enough to prove us actually Zoro could have hurt seriously Kaido if even Big Mom asked him to dodge.
Being never targeted means they can't face a top tier or kaido ?
Zoro is facing King the guy who is the strongest after kaido, who tanked his onigiri with haki post rooftop, that says a lot. The same King who has 0 wound after facing Marco for a decent amount of time.
If Marco can stall true top tiers, then king who is also his rival can stall any top tiers. So finally Zoro who is probably above or in any case equal to King can definitely face any admirals and yonkou at this point of story.
Oda just confirmed again One Piece gonna end soon and you think in 2 or 3 arcs, Zoro will jump from being not capable to face Kaido in 1 vs 1 to be above or equal of Kaido at EOS ?
If Luffy, yamato, law, kidd or anyone are Kaido or Big Mom in 1 vs 1, Zoro who will defeat another world strongest in few arcs can definitely do better than what you think.
But the difference Zoro won't go only to stall because with his AP, he can literally murder anyone without plot armor.