If you are for example the only one engineer in a team and enemy tank is coming you have almost no chance to fight that tank with RPG (only a couple of mines on the ground can help, but mines can be easily destroyed by anyone) .
Like in real life tanks are powerful (that's OK) but if you have good RPG you should be also allowed to destroy a tank by one hit. The same applies to jets. Jets when navigated profesionally can easily destroy infantry with bombs , but if you have stinger you should be allowed to easily destroy jet also.
But again, with powerful RPG and stingers we should have FASTER spawn OR BIGGER NUMBER of vehicles accessible on the maps otherwise it is a fight for vehicle - many players want them and you cannot get them.