are you talking about 5 thick? Because at that point you would have no room inside the structure to really move if its in a doorway for example.
As far as how much a TNT should take out, that depends on the space between the structures and the TNT.
If its placed DIRECTLY on it, I could see it going through 2 layers pretty easily.
Also keep in mind that replacing those front structures isn’t as easy as you might be thinking. Sure the initial placement will hold the enemies back for a little longer, but stacking them as thick as what you are talking would actually make it HARDER for them to be replaced.
Ultimately this means thick stacks last less time and are harder to defend.
In the current state of the game, large caliber tank rounds (HE) will take out sandbag walls in a single hit. If they were made to be 2 hits, I think it would be fine.
Smaller tanks may take 3 or so HE hits to knock down sandbags walls, but being smaller caliber and with a loader, that really isn’t that long.
This is assuming that players are stacking them 5 deep, which as I explained before is unlikely to happen.
In addition, if you are the ONLY thing hitting them, then yes it may take a little bit of time, but the chances of being the only thing hitting them is also quite low.
Please also note, another thing they could add, as it occurred in real life, was to use the tank barrel as a battering ram as sorts to push through sandbag fortifications. Something to think about.
You’re only talking about extreme cases of spam, which in Majority of games simply would not occur.
Currently, playing as offense is extremely easy in comparison to playing defense.
There are far more tools that are effective for offense gameplay in comparison to defense. A solid 4v4 of equal skill will nearly always win. in favor of offense.
Even games where the defenders are coordinated, and the attackers are not, the attackers have spam tactics that keeps defenders at disadvantage, despite having “infinite lives”.