I have to agree with @dwooten77, a lot of times whether or not you get repeatedly trampled by another particular character type will depend in part on what character you are playing yourself, along of course with other factors like skill comparison, terrain and variables like general combat chaos.
For myself personally some of the characters on your list can be problematic but generally the reason I find them so is due to the character I'm currently playing not being a suitable foil for them, with a close second being that I'm distracted by trying to accomplish a particular thing.
Generally speaking in a game I give as good as I get even against characters labeled as "OP" or "Broken" and it's rare that another player gets ahead of me enough to become a Nemesis when I'm playing a character which I'm comfortable with but when it happens I just shrug it off because it's not worth souring your entire attitude over. Heck, it happened this morning with a BBQ Corn player getting 1-9 over me while I was trying to level up my Sanitation Expert by coming in repeatedly from the flanks while my attention was elsewhere but I'm not going to say that it happened because of the character because in the same game I managed to get matching vanquishes with other Corns and managed to make a Hot Rod Chomper player really angry with me by going 7-1 against him.
I agree that the "instant arming" Spikeweed is a feature which can be considered Broken since it's a radical change to entirely remove the arming time that it had in GW1. But as far as other characters are concerned I don't personally consider any of them to be overpowered- I've frozen an oncoming Z-Mech as easily with an Ice Cactus as I have with the Frozen Citron and I've done equivalent feats with the Arctic Soldier and Goalie Star against the Plant team.
My own view is that different variants have different advantages and some of those advantages are easy to access, like fire, ice and toxic effects, while others need more skill or experience to use to their full advantage.