Top Lane Mana Costs

Maybe it's just me (I'm only gold here) but I feel like the reason top lane juggernauts are performing so well is just because their mana costs seem to not hold them back much. Fiora and Darius seem to be able to trade for forever, while Irelia, Jax, just can't. Maybe other bruisers are adequately mana restricted and the new juggernauts are too mana efficient, or other bruisers' mana costs are just outdated, but I'm convinced that the problem with top lane right now is just mana costs to trade. Maybe this is also not a priority heading into a new season, but when Irelia uses 90/95/100/105/110 mana to trade with a Darius while Darius is only out 60/65/70/75/80 mana, AND Darius is getting full mana refunds on his farm w (not even considering the cd return) while Irelia is getting .5 the cost back on her q (with no cd help), that just seems inherently wrong. Not saying all top laners need to have the same costs, but the difference seems way too large in my opinion.