Sadly as a OKW player you are forced to crush buildings with your trucks, since you can not clear buildings with your units until fuel intensive units arrive.
Every faction has a flame-thrower with exception of OKW.
Yes OKW are forced to play like this. Try playing OKW vs Soviet on maps with good building positions for maxims and demos in buildings. OKW flak HT can barely clear one MG from a building before it has to retreat for repair. ISG? lol what. Stuka? Yeah its a great late game unit but early game 1vs1 it's way to risky investing that much into AI.
Soviet on the other hand just need to spend 15 munitions to clear a building or place a demo for a squad wipe since OKW suck at clearing mines/demos. So until OKW get a more reliable non-doctrine way to deal with buildings early game and/or remove demos from buildings I would say this truck abuse is fair play.
Every faction have something to abuse but as usual its easier to deflect blame rather than to accept the fact that the vast majority of top players are abusing the game, more or less. It's not the players fault but poor unit design. Alot of it could be fixed with a few tweaking but instead Relic listen to the COH mob that scream nerf this and that.