No, they are not.

With the possible exception of some of the aircraft some carriers are retro-fitting with over-sized OH bins, there is simply not enough OH room on a standard domestic narrow body aircraft to accommodate all of the "legal" bags allowed. This is far from a DL problem and occurs on pretty much all carriers in some form. There are three solutions all of which presume that DL strictly enforces whatever policy it chooses (which also leads to rants from people who have over-inflated views of their value).

1. Cut the allowance to one piece of a dimension whereby there is enough space for all passengers.
2. Cut the allowance for some segment of passengers.
3. Permit the current allowance and simply start checking bags when the OH space runs out (current practice).

One can argue the merits, but what one can't argue about is the geometry.