It could be because the boulders no longer have AOE damage, and so its misleading from what you would expect. Only one building part will take damage.
I tested in single user and there, the boulder always damages something. It’s clear to me that the boulder is almost useless, and at a higher cost, thus I’ve not bothered to use it for real in online other than to trial for aim. Its also possible that online its different (and worse like you reported) from what I found.
Trebs are nerfed big time. A whole thread on that topic here…