I agree, if you want to enforce the turn system strictly, but in a lot of games a turn involves taking just one action whereas in D:OS you can take multiple actions each turn, which doesn't make sense in regards to time lapse. If you do not like the idea for some reason then that is what is important.
Naaa, the "one action per turn" TurnBased-System never overs the tactical depth what a action-point based systems over.
Look at the original XCOM, Jagged Alliance and the dump down current remakes.
if you want a TBS-System that makes sense (regarding to time lapse) you need a wee-go system like used Frozen Synapse or Combat Mission. But i think this don't fit here.
IMHO: AP based system offers the most opportunities for balancing and tactical depth