I did playtest it.
But without the creation rules I cannot playtest two characters that are identical except for class.
Have you tried adjusting character abilities and then adding up the plus to hit and plus to damage? If you actually do the math with the sheets you will discover some bonuses included for certain characters that don't appear to have a cause. These will be revealed when the playtest of character creation comes out in a few months. Meanwhile there will definitely be differences in the to hit and damage areas even if the stats are identical.
The reason according to Mearls and others in chats, interviews, podcasts, and articles on the Wizard's site - class and race modifiers.
So yes, you could playtest characters with identical ability scores without having the character creation rules in hand. Admittedly, it would be more fun to have those rules to mess around with, but to see what we've been discussing you don't need them.