For instance, what if there was some sort of 'inertial dampener' upgrade that allowed units to disembark when moving flat out? And what if the Wave Serpent's energy field extended some sort of protection to the dismbarked unit, if neither moved away? That would better enable them to present a threat in just that way - and in doing so, would become part of a style of play where you had to plan ahead and have units support each other, which we Eldar players always seem to be going on about anyway.
That's just an example off the top of my head to demonstrate that there are other ways of doing it. And anyway, a flat out Wave Serpent is hard to kill, especially if you Fortune it - it's not like an ork trukk coming at you. If it was an assault vehicle as well, you'd be looking at a point and click auto-squash of a unit of your choice - move your tank forward, the enemy rolls some dice, if they get the right result on the dice they're fine and if they don't they're dead. We like to think that Eldar should be a finesse army, but if we're going to truly believe that, we should have the courage of our convictions, not resort to asking for 16-point models in a 100-point tank who can splatter almost anything they feel like with the ease of terminators in a Land Raider. Where's the fun in that, for either player?
And after all that, I have to say that I'm not really convinced that Aspect Warriors and Wave Serpents are cripplingly underpowered as it is. There's not a lot there that can't be fixed with points values - I don't think they're unfit for purpose particularly.
I think you've misunderstood my reasons for posting all this - you seem to have assumed I'm a marine player trying to jealously guard my special rules. I'm not, I'm an Eldar player who would prefer my army to play in a unique and appropriate way, rather than cave in to 40K's flaws.