I don’t think OP claimed any of this, at least in my reading. All of these things are trade offs anyway - a weaker immunised patient might become a training gr

I don’t think OP claimed any of this, at least in my reading. All of these things are trade offs anyway - a weaker immunised patient might become a training ground for a variant, but a weakly immunised patient might also have a reduced risk of spreading which results in fewer cases and fewer chances for mutations.