@asabaida Riding the boss isn't as advantageous as it sounds. I too was worried that if you can ride a boss that it could be pretty crazy. It certainly seems like it would be insanely good at first glance but in practice it's far better to ride a normal teammate.
The armor does help but all the plants have to do is rip the wizard off. I tried riding bosses twice last night in a weekly event match, once on a disco boss and once on a gargantuar. Both times I was sniped off very quickly as the boss will just stop moving to attack often, making you very easy to shoot off. Even when bosses do move they don't move very fast and the disco zombie boss's invulnerable spin does not protect any co-star rider. They also don't use cover unlike your teammates and have no sense of self-preservation, making you very vulnerable.
Bosses also are not player directed and just wander about instead of trying to focus or team up. This makes joining with players more tactically useful. I played both sides several times last night and having 2 sunflowers latched onto a sunflower queen boss was far harder to deal with than a co-star on a zombie boss's head. They also don't use the tactical intelligence starz align provides and will casually head off away from plants I was able to see before they turn. You're at the mercy of the Boss's AI and while they're tough and can hurt, they aren't exactly tactical masterminds.
Honestly, the idea of several wizards staggering their zee-lixirs to extend their effects beyond the normally short window was much harder to deal with than riding a boss. I know we had 3 of us do that in a row last night, even without pre-planning. A group of wizards timing this well is probably the most dangerous thing with them right now. Bosses are immune to being goatified and chomped and disco zombies can make themselves invulnerable on their own. Zee-lixir does seem like it cures a few too many things but a single zee-lixir use every 20 or so seconds isn't a huge deal, a squad of them can be extremely powerful if played well.
Of course with plants being plants and some fungi, having a plant class in future based on a symbiotic idea could work in future with a similar idea to the co-star.