(I should share a definition of balance that I encountered that I've found helpful
A game is better balanced the more choices it presents to the player that are both meaningful and viable.)
The point is just that the game has imbalanced classes. The reasons that could be bad in a cooperative game are myriad and have often been belabored in the past.
But, whether it's a 'problem' is more a matter of point of view. Imbalance is not a problem for a game producer if it does not demonstrably harm revenue. It's not a problem at a particular table if no one takes an over- or under-powered class (or if everyone takes either all one or all the other - it could be a problem for the DM re-balancing challenges to match), because you're playing a "balanced" sub-set by eliminating choices (which is not actually better-balanced, just more up-front about it). It's not a problem to system masters who optimize the best possible choices for maximum power (OK, it may be, if it's too extreme) - or knowingly optimize a bad choice for the challenge (unless, again, it's just unsalvageable). It's not a problem for a player who happens to choose an OP class and enjoys playing an OP character - which may be a problem for other players at the same table. It's not a problem for players at a table where the DM goes above and beyond to fix/mask/compensate for balance problems (tho it's an added burden on the DM, some DMs can handle it).
So, yeah, there are cases where imbalance may not be perceived as a problem. In most of those cases, balance wouldn't be a problem, either. System masters for instance, relish optimization in a better-balanced system (with as many or more choices than a comparable imbalanced system), even tho the gross rewards are smaller, the challenge can be more engaging. Players who would normally all gravitate to sub-sets of choices that avoid imbalance have the full set of choices available, instead. The player's at the great DM's table won't notice a difference, tho the DM may be a bit relieved. About the only ones left out are those who just pick OP options on a whim and are happy to be OP.
Balance facilitates that. Balanced choices give each player a better chance of playing what they want, without overshadowing others or under-contributing.
Balance doesn't always fail by presenting meaningful but non-viable 'trap choices' or overpowered choices. It can also fail by offering meaningless choices. "Are you a member of the Wizards of the Aubergine Order or the Purple Sages of the Royal Palace?" What's the difference? " The color of your robe..."