I mean they are allowed to have their opinion considered. Obviously they're allowed to express it.
How do you disallow someone from considering someone else's opinion? You can't. Most of the common rhetoric about opinions doesn't actually make any sense.
The reality is you can think what you like and that goes for everyone else too. As for expression, you can say what you want if you keep to the forum rules.
If you're using player feedback (even in part) to build a balance patch then you've got to account for everything that influences that feedback. That feedback is in part affected by the unit's actual performance but it's also influenced by other things. Personal bias, RNG and player skill level to name a few.
To gauge the unit's performance you've got to find a way to filter out these other things. The feedback of high skill players is most useful for filtering out the influence of player skill. It can still be biased which is why you listen to more than one player: if a large set of high skill players broadly agree on a unit then you can be fairly confident they're onto something.