My opinion on this has always been that there has to be a slightly longer spawntime on both sides. Spawntimes are a big part of balancing in this game since defence always has a couple advantages. The heavy weapons don't bother me because it's part of the game and the players who use them usually don't know how to use them effectively. Plus in etpro they are usually used for spawn killing when in a positional advantage which isn't allowed.
Back to the spawn times, I feel like slightly longer spawntimes won't unbalance the game all that much, especially with higher numbers of players. Something like 26-defense 18-offense feels pretty good and not at all overdone, seeing as most maps have their game times at 25min anyway. It may also discourage more spawnkilling as accidental encounters won't be so common either. A lot of maps like Frostbite, Beach and Goldrush are made with spawnaccess for the allies since it's part of the objective. With low spawn timers it gives the allies an extra disadvantage on those maps because they can't use the spawnway anymore, even when they are already so Axis sided.