On one hand, the argument against the under-barrel weapons is valid: impossible to see and plan for as a xeno. But also, it’s really that big of a threat only for the highest risk castes(read: runner).
On the other, there’s been a big trend towards simplifying the infantry gameplay almost to the point where it’s “hold LMB”. Anything more complicated than that gets nerfed into irrelevance. Under-barrel weapons are lore-friendly and add complexity and variety to the basic infantry kits. That, for me, is exactly enough to outweight them being slightly unfair.