Rhinos shouldn't get assault vehicle because SM's already have two assault vehicles available to them. There, thats settled. What is up with this marine relativism anyways? Why should a rule that applies to a falcon apply to a rhino anyways? What the hell are you talking about? I don't follow your logic at all.If Falcons get Assault Vehicle, then Battlewagons with 'Ard Cases should definitely get it, and Rhinos should get it as well. There's no argument you can make against those that wouldn't apply ten times more to a Falcon.
You're saying that the falcon shouldn't get the assault vehicle rule because its ... a tank? The recommendation to buy a DE vehicle for my banshees is laughable and doesn't even merit a response.
Assault isn't going to be "fixed" in any meaningful way. Its obvious that the rules designers wanted it to be difficult to assault out of vehicles and they bestowed the ability to assault out of vehicles to certain units for every faction where assault is actually a thing you want to do. The Eldar book doesn't have that ability for some reason. Its certainly not because the units being delivered are too strong and don't warrant protection. Its not the only reason why Eldar assault doesn't exist in a meaningful way, but its a contributing factor.