Its not just that TW vehicles are 'hard', its the asymmetry cutting into the gameplay. For context I played with TW vees a LOT in both narrative games and competitive games. But, when I play with and against vees in a balanced game, the first thing is '6 units max'. TW vees and infantry spamming 40 units versus 4 mechs is just a problem. No not everyone does this, but even if you are not spamming on purpose, you get just SO MANY MORE units with vees and infantry. I remember in my long running campaign rolling up an infantry force for my friend's campaign lance as opfor, and I was excited for all the field guns, APCs, and different infantry units. But the vees and infantry just were not fun in that quantity--and that was a narrative campaign without balance concerns, thus giving the infantry and vees the best shot to be fun. Instead, it was just a chore.
Now, with BSP, im having WAY more fun putting dozens of BSP units on the field. They play better, arnt exploit-y, and integrate MUCH better with initiative, and they play FASTER, which is huge. 2 steps to move all BSPs before mechs is a great thing to solve the unit count mismatch, and for fun games I dont have to institute hard unit limit caps to enjoy my time.
So its not so much the rules complexity, its the gameplay loop--especially with maintenance and such--that surrounds TW vees and infantry. Also, 'hero' tanks being played per TW rules as part of your '3k' BV of player forces I think does a great job filling in the cracks, if you really want a Manticore Tank Commander for example, backed up with some BSP Manticores and a Mech.
The Mercenaries box set campaign loop (now found in hinterlands) plays really well with the size mechanic, providing 1-2, 2-4, and 3-6 'real unit' game sizes (size 1,2,3) with BSPs for flavor that dont clutter the initiative unit count. Having some TW vees in your 2-4 'real units' you track is fine, but the other 6 vees you would normally get are BSP to keep the game moving at a good pace.