Your reasoning is not stupid by any means but it rests on the assumption that haste is always your best stat for all scenarios.
Crit is the most efficient stat for a resto druid beating out even haste if you consider mana, the only reason haste is our best stat in a pawnstring is because it measures raw throughput and haste double dips because of the GCD-reduction it provides.
That basically means that haste is amazing if you have infinite mana but the only time where that is the case is in mythic+ where mastery is even better.
In terms of mana efficiency haste is actually our worst stat being like 15% below versa.
If you use pawn for upgrades then I would suggest using Torty's spreadsheet where you can get more exact values for your character. Can't link because I'm new.