FlemFire

I don't see recon or scouting anywhere in your tactics there.
Generally speaking, if you have the appropriate resources at your disposal, then patience, reconnaissance, and applying firepower will work in your favor. Personally speaking, impatience is my #1 error. In your example the enemy has too many points to cover your angle of attack. Don't try and establish a base of fire on an enemy that could return fire from superior positions the second you pop your head. Smoke screen. Or apply harassing artillery support to soften them and then follow through with suppression via on-map resources. Those are just examples off the top of my head. 99% of the time if something goes sideways in CM it is, on reflection, wholly my fault and there usually was a better way. And the best way to learn is to just make those mistakes and then think about them and figure out what could have been done different.
Sometimes scenarios/campaigns are designed to be considerably more constrained, surprising, and/or difficult, but I suppose knowing the difference between "I'm messing up" and "the scenario is designed to mess me up" is a whole 'nother bag of hammers.
 

I don't see recon or scouting anywhere in your tactics there.
Generally speaking, if you have the appropriate resources at your disposal, then patience, reconnaissance, and applying firepower will work in your favor. Personally speaking, impatience is my #1 error. In your example the enemy has too many points to cover your angle of attack. Don't try and establish a base of fire on an enemy that could return fire from superior positions the second you pop your head. Smoke screen. Or apply harassing artillery support to soften them and then follow through with suppression via on-map resources. Those are just examples off the top of my head. 99% of the time if something goes sideways in CM it is, on reflection, wholly my fault and there usually was a better way. And the best way to learn is to just make those mistakes and then think about them and figure out what could have been done different.
Sometimes scenarios/campaigns are designed to be considerably more constrained, surprising, and/or difficult, but I suppose knowing the difference between "I'm messing up" and "the scenario is designed to mess me up" is a whole 'nother bag of hammers.
 

Why would small-arms fire be effective in killing people in buildings in the first place? Unless you can shoot through the material it's unlikely that your bullets will find targets, and even more unlikely when the enemy becomes pinned down. Your troops are basically shooting at a vague silhouette standing behind blocks of concrete. If you spend 9mins shooting at someone in a building, you probably could have spent 1-2mins doing that while simultaneously moving an element forward to properly destroy the target.
 
Personally, I find buildings to be death traps if the enemy has explosive weapons. Like in SF2 for example, if I hole up in a building and the enemy splashes it with an RPG I'm liable to lose a team or an entire squad.
 

7.62mm NATO when fired from a GPMG will go through breeze blocks and bricks in heartbeat - so some small-arms fire would be expected to drop people in buildings constructed of those materials.