Proposal for a compensation buff to hecarim's passive

It's a simple buff, nothing gamebreaking. To emphasize his identity as fast ghostly steed that gains damage based on his movement speed, why not make it so he gains bonus ad based on bonus movement speed BEFORE the diminished effects to movement speed.

So let's say hecarim has 415 movement speed, gains a 50% ms buff. That should put him up to 623 or so right? Wrong. That would bring him to 554 movement speed. So he gains a whole 25 or so less AD because the calculation is based on the 554 movement speed. My proposal is that his passive should be similar to thornmail in that the bonus AD is calculated before the reductions in movement speed.

What would this do? It would discourage hecarims from trying to be moving hulks of health and defense and instead encourage them to try to build around his movement speed playstyle allowing them to build more damage without feeling that their passive is utterly lackluster.