Tell me where there is a perk (what are you talking about with stats? there are no stats. stats=attributes) that increases mana regeneration or overall movement speed.
Attributes govern how well you can perform your skills. perks are simply little bonus features, such as "increased arrow recovery" or "chance to disarm opponent", though not limited to those, but that's the way it should be. Attributes could also govern how well you can perform your perk bonuses as well!
Because it provides balance to the gameplay. It adds a sense of realism. You'd expect a mage to have a high intelligence than a warrior, or a warrior to have a higher strength than a mage.
I can see where you're coming from with "well, now it's just that we expect mages to cast magic and warriors to use swords/ages/maces".
But without attributes, now it's just "oh, you want to be a warrior? well, do you want to use an axe or a sword? light armour or heavy armour?" instead of "do you want to hit harder, or do you want to move faster, or a balance of both? do you want to use an axe or a sword? Heavy armour or light armour? If you choose heavy armour, do you want to balance the speed restriction with increased speed attribute, or do you want to maximize your tank ability by increasing your endurance and physical resistance?"
It simply adds another element of customization to the game. Without them, the game just feels boring and our characters are forced into tighter molds that restrict our freedoms.
There you go.
The point is still, even if there would be a way to change speed the "old way", it can be done without any "speed" attribute.
Light armour and heavy armour are exactly the same, end-game at least, provided you choose the perk that makes them weightless.
And sprinting is not the same as increasing your maximum speed. It's a short burst of energy that makes you run faster. I like it, and I'm glad they finally implemented it in the series. Speed is an OVERALL maximum increase in movement. There is a difference.