Pinned tier lists from Ogryn Discord.
First the one for without a Vet on the team:
Now the one for with a Vet on the team:
Notice how both have Cleaver in S Tier? Stubber makes it into S on one A on the other. Ripper gets into A on one and B on the other.
My point here is not to say that you are categorically wrong, but that your statement is not universally true either. Generally weaknesses of your melee weapon can be covered by ranged and vice versa. For Zealot you have a built in way to deal with Crushes with flamer and brauto (2 of the most popular Zealot ranged options, neither deals with Crushers well if examined in isolation). Psyker can cover armour impaired melee with Surge, and can cover Purgatus armour weakness with FS or Caxe. Rending shockwave on Trauma (which actually applies brittleness description wrong lol) can significantly soften armour weakness of your melee.
So on and so forth. It’s correct to say that bringing a loadout that has no anti armour capabilities is a poor choice. The same cannot be said about individual weapons without taking them out of the context of the rest of a build.