All melees have positionals, NIN is no exception. Unless SE decides to make it different, all melees have rear and side positionals on several abilities. So remove Armor Crush, and you basically just have to stick to the enemy's butt 100% of the time.

DRG also has a DoT/debuff combo (Chaos Thrust), and a plain damage combo (Full Thrust).
NIN's Armor Crush is pretty much the same thing as SAM's Shifu: a 30s haste buff.

Imo, pressing sometimes 1-2-4 instead of 1-2-3 doesn't add a lot of depth to the gameplay. But in this case it forces you to deal with positionals and move to the side, then back to the rear, which adds a layer of player's skill. Get rid of Armor Crush and you make NIN easier to play, not only "less clumsy". Not that it's necessarily a bad idea, NIN is hard to play (for me at least QQ)