Why would ditto have that ability when it can just use transform?
Using transform wastes one turn which gives your opponent an opportunity to
give ditto major damage. When ditto has imposter, It also copies all moves
and types but you transform as soon as ditto is placed in battle.
But since ditto is slow and if it doesn't have imposter, give it a quick powder.
Hoped this helps
Well, Ditto is a gimmick, and I suppose people have been complaining, so now Ditto can have Imposter as Hidden Ability, and Ditto would viable in the competitive world as a revenge killer. You won't have to waste a turn.
Hope this helps!