Scale is absolutely fine. Scale gets +1/+4 with each upgrade and plate gets +1/+5 and starts a little higher. You're much better off not throwing away upgrades you put into scale in order to make the switch. Now, if you have scale +4 and find plate +3, and you have upgrades to burn, sure, make the switch. Those armors at that point are about the same, and putting upgrades into plate is better.
With a ranged class, I sometimes beat that game with just chain mail. With melee, you can beat the game with only +4 scale. You just put more upgrades into weapons and wands so you kill things faster or have good utility. "The best defense is a strong offense." (Unless you're playing berserker, which you should not do except to get the badge maybe.)