In about 90% of cases that I see radio operators being used, its by a guy that has a sniper and engineer in that squad also, and they are sitting in the back or at the side of the map, raining artillery every 2 minutes.
In comparison, I almost NEVER see the actual Radio Operator SQUAD (identifiable by them having 2 radio packs in the group), moving toward the objective.
Pay close attention, as you CAN identify which direction exactly they are coming from it makes them quite easy to locate.
The mortars have to have access to the open sky.
Otherwise the shell will hit the wall or ceiling, drop to the floor, and soon detonate, killing you.
In comparison, Radio Operators can make artillery calls from absolute cover, and not have to worry.
In my experience, mortar squads are rare enough to begin with. Most people don’t bother trying to take them out so they usually don’t really even try too hard to conceal themselves. Ammo boxes are often clustered up at least 3 around them, sometimes I’ve even seen 6 boxes if another player sets them up for them.
A big cluster like this is even visible from the air.
Speaking of the air, if you fly over the area where mortars are being fired, you can often hear the mortars whistle near your aircraft, letting you hone in on their position quicker.
I know this takes more intelligence than your average run-and-gun player to figure out, but the point is that mortar squads are considerably easier to deal with than radio operators.
Unless its a DIRECT hit, or multiple hits within about 2m then no, they do NOT destroy fortifications.
In fact, that is one of the biggest draws of the 80mm mortars in Berlin. They can more effectively destroy fortifications (still requiring very close hits to fortifications but just less hits to destroy) and can even kill tanks with DIRECT hits.
The same effect that artillery strikes have against tanks, but without the fragmentation radius that the artillery strikes have that wipe out every structure and most infantry nearby.