Ok, let me put it another way: Think about how your suggestion will affect the rest of the game before suggesting it.
There, is it easier to understand now?
The answer is still yes. The specific reason actually differs between each class tree but the argument stands that if your low rank class skills are effective enough why bother with higher rank ones at all (especially if you’ve already invested in attributes of those low rank skills)
Care to go into detail? How is a skill with 25 hits on 5 second cooldown and over 1000 skill damage at max rank not as strong as them?
Actually, care to define your definition of ‘viable’? To me viable is something that still have uses, but I don’t limit that definition to combat only because that’d make Squire/Pardoner/Alchemist ‘not viable’ (Squire c3 would limits you to only rank 1-4 of the tree)
Also, while I don’t know about the rank 3 classes, I do know Cryo 3 Elem 3 is ‘viable’ in earth tower.
I can’t be bothered to dig up which interview it was, but the Dev said they made skills don’t scale to avoid people having to deal with too many hotkeys.
So unless they’ve changed their mind (which I’ve yet to find any evidence of such), yes it is by design.