Why would you have to have forced side balancing if ENY was removed?
Because people would complain.
ENY does not make people change sides that I've ever seen. Only a very small percentage of players have auto-side switching enabled and those are the only people I ever see changing sides.
Most people sit in the tower waiting for ENY to change, or they will fly a crap plane that they don't want to fly or they will log before they will switch sides.
I typically switch to the low #s, but the issue with that is the switch timer far outlasts how often a side numbers can fluctuate, or a fight dies or the front moves. More enemies and cheap jets, what's not to love? There are downsides to the side switching option. Like I said, personally, I don't like it, nor do I use it.
Again, I'm not sure what sort of "crap planes" you're referring to, but unless ENY is sticking you in 30+ ENY planes, the majority in the 15-25 range are just fine.