But "levelling systems" is a permanent core in games now and will always be there. Progression / persistence and unlocks is as much a part of the game core as the maps are, or the menu. So you can't dedact that from the equation.
Classes still have their roles in BF3 though, it's not like anyone can become exactly what he wants with all classes, is it?
I also consider what "kit" the player has to be a minor balancing parameter. The heavy balancing factors should come from how the terrain is built, the level design and what vehicles the designer gives you.
Breaking it down, balance should come from a model looking like:
Terrain formation: 20%
Static placements: 25%
Vehicles/ assets on map: 15%
Soldiers individual strengths: 20%
Players individual "skills": 20%
These numbers are grabbed from thin air just to prove the idea of the model. It basically mean a very powerful soldier (all ulocks, all geared to the teeth with the best stuff) and a very skilfull player (on a high-end rig with low ping) still won't be able to "ultra-pwn" another player if he has the map (terrain/positions) and map assets to his advantage. However if he also has the best vehicle, he'll crush the opponents even if they have the best position (>50%)
However a "low skilled" player who uses the map design and the assets to his advantage, will win over the highskilled/maxed out geared soldier (40% v 60%)
Design must take these rock-paper-scissors concepts in to practice, or the game will become too predictable and static. The game and the map should always be the over-weighing factor, if you use it well, you should get the upper hand, IMO
Consider Counter-strike as comparison. Their model could look like this:
Terrain formation: 10%
Static placements: 15%
Vehicles / assets: 0%
Soldiers individual strength (basically what weapon you buy in the beginning): 35%
Players individual skill: 40%
It does mean, that a low skilled player (like me) could win against a high-skilled player if I had the best weapon and had the best map-position advantage on him. However if I meet him in a straight corridor with equal cover, Im fragged, 100% of the times. It also means that if he has a better weapon, Im unlikey to ever get a kill on him, even if I use the best covers / routes.