There's no point destroying more cover if you don't have anything with which to fire into the gap.
I completely agree with you on this, but I rarely if ever see anyone play with this in mind. Apart from that, I notice that people generally don't use rockets as anything but pure offensive weapons; they don't use them to open new paths through structures for themselves, or to deny enemy players good positions. They spam them through every opening on their side to destroy the buildings and walls on my side. I have two options: Allow them to do this without responding in kind, in which case they've got a line of walls for their units to hide behind, popping out to shoot, and I've got an open area with little to no cover; or act with the same idea in mind, just to prevent it from working for them. If both players are using their rockets to wreck the cover on the opposite side of the map, pretty soon there isn't much cover left. It isn't that either player is wantonly destroying structures for no reason, as there is a very clear purpose. It is just that neither player can afford
not to destroy enemy cover if they want a chance at winning the match. Rocket matches almost always (in my experience) end in the same result, and I honestly can't say that that is a good thing. It has gotten to the point where in a match with rockets, I can usually predict the first three shots they'll take, and plan my positioning according to that. Not the "Oh, I know the logical places for them to move to or take cover at, let me try to set up to cover all of them" that you get in a normal match, but "They will shoot here, here, and here, unless they're completely stupid".
The
only uncertain element of a match with rockets is the unpredicability of whether or not the other player knows how to hit light cover with them.
As I mentioned before, I see two approaches that could make rockets an actual tactical weapon, rather than spam: Limited ammunition, or replacement with a different unit armed with a limited number of timed C4 charges (and a pistol) which would fill the same tactical roles as rockets (opening new avenues of movement and firing, breaking up easily campable rooms) without allowing for excessive spam. For that matter, I think the same approach would be good for the grenadier: A unit armed with hand grenades (perhaps 3 fragmentation and one HE capable of destroying light cover?) and a pistol, which again fills the tactical roles (clearing rooms you know are being camped) without letting people spam explosives to excess. With both, you've got the tactical capabilities of the former unit without the potential for a match filled with spam.