This topic brings back memories of abusing the hell out of mines (when it was allowed of course). Yes, I was one of 'those' players that would get bored with how a match was going and would recruit others on the team to proxy mine harvesters and any vehicle that went out of the base. Often it was for defensive purposes only, honest. But there is a downside to doing this. For every vehicle covered in proxies there's that many fewer mines to defend a base.
When the enemy team started mining their own vehicles we just switched to rushing undefended corridors while ours were mined again. It's all in how players go about things. I think a transport chopper was rigged once to clear the intended LZ. Think of an exploding rock dropping out of the sky.
Anyway, there is always the chance for players to abuse game mechanics. Even without proxies rushes can be done against expensive vehicles. Just load up a vehicle with free engineers with C4 already equipped. Rush the expensive target like a Mammoth Tank, and when the cheap delivery vehicle explodes everyone rushes and throws C4 on the tank. They die, the delivery vehicle is destroyed, but that tank is probably toast.
The hardest part of figuring out what to do about mechanics being tested by players like with C4 Rams is to do it in a way that doesn't break what they are supposed to do or more 'legitimate' uses like defending a harvester against walkers. I've got to say, fixing this one is tough and may involve something like if two vehicles have proxies on them, one from each side, the proxies exploding on both will partly cancel each other out. Think of it as a reactive defense system against rams. In effect, make a C4 Ram to protect against a C4 ram. Either that or have free meat shield characters move out in front of expensive vehicles to create a protective barrier.
Or an even better solution. Give tank rounds the ability to detonate C4 mines located on other vehicles. One shot from a tank at a charging C4 Ram will cause the ram to go up in smoke. Rams are defeated and mines aren't nerfed.
Personally, I think things are fine the way they are. A-symmetric warfare is one of the things Nod does. Rig up dirty tactics to use against the superior arms of GDI. Why not let the spirit of Nod's tactics be reflected in RenegadeX or allow GDI to simply throw it right back with tactics of their own?