I don't think the lack of Spawn on SL would change the balance much since both sides would have it. It can slightly as it's set up now, since it allows players to spawn out in the open. I think attacking SL's are less likely to be in a protected space resulting in more squadmates being mowed down.
As I stated earlier, if it was more limited in where it was available, it'd be less effective as simply a forward spawn point and more as a way to gather your squad. If you couldn't use it unless you were in hard cover and more than say 80 - 100m from a cap, you wouldn't see enemy spawning behind you, or right in front of the cap. Either side could use it both to increase squad effectiveness or for strategic reasons. You could use it to build a force to push a flank or unexpected area. SL's would then have an additional choice to make, get a squad together for a coordinated attack, or try to get in the cap themselves. Or first one, and then other. With limitations, it wouldn't be used as haphazardly as it is now, but with a more logical effect.
You could argue that it's not needed, that SL's could do the same today by calling out to their squad, "meet me behind the tank in G6 and we'll attack the barn". Anyone who's spent anytime on a public server would know that with the pace of the game (get in the cap!!!), the difficulty of locating squadmates in Classic and the slower movement speed, it's unlikely anyone would spawn, and then trot across the map hoping to find their SL. It needs to be easy for players to buy in.
I also like the fact that it allows spawns to change, do you really want to always know exactly where the enemy is spawning? Have you ever played a game where you don't? Except out in front of you somewhere? It's far more tense and allow maps to play out slightly differently. By now, everyone knows which caps to attack first on each map which is based on where you can spawn, I'd like to see things mixed up a bit. Even Winterwald the most open map; A first, then B. Each and every time.....
It would also allow spawns to move out from under arty, (yeah it happens) and away from oppressive fire. (Spawnraping is less common in RO2, but it does happen) Anyone ever been on the wrong side of an asskicking in Kessel or Grain Elevator?
I try to look for unexplored potential in existing features and find solutions when they are less than optimal.
I believe the main reason that maps are defender biased in Classic is the difference in movement speed and stamina. In Realism, attackers can obviously cover more ground faster, but are also harder to hit since they can zigzag liked crazed squirrels out in the open. Add that sprint to IS is also available and they are better equipped to assault than they are in Classic.
