You can certainly hide literally anything you see on the screen with CSS rules applied to the site’s theme at will … but this (basically, force everyone to leave comments with all flags except spam?) is a somewhat unusual request I haven’t heard before.
The idea of the “something else” flag is that something nuanced is going on which requires explanation versus “hey staff, please point your attention in this area for a moment.”
I suggest that, before proposing big changes, it might be better to give things a few months to stabilize and for everyone to acclimate to the change in software. To get real world experience and gather data, if nothing else.
(That being said, I am definitely sympathetic to anything that makes moderators’ lives easier – that is, and will always be, an explicit goal of Discourse. If you are seeing a lot of inappropriate / troll flagging, we can advise you about that, but be advised there are already systems in place to deal with that, e.g. staff disagreeing with a flag automatically lowers future flag weight for that person.)