I didn't find their tactics partricularly stupid. It was a basic castle-defence plan of falling back by stages, and taking as many of the opposition out at each stage as possible.
The Dothraki were a mobile force, and temporarily powered-up with flame weapons. Having them make a lightning strike against the enemy frontline wasn't a terrible choice - the only other thing they'd have been good for was harrying the flanks once the armies were engaged, and there was simply no way to coordinate that in pitch darkness.
Lighting the trenches any earlier would've been counterproductive - they would have cut off the retreat of their main forces, and would've burned out half their fuel by the time the horde finished cutting through the Unsullied.
The pacing does get weird after the army breaches the walls, though. It goes from pitched battle in one scene, then when we next cut back it's all sneaking around in corridors. It feels like there was supposed to be something in between that would have slowed or diverted the horde's incursion, which we didn't get to see.
The really big thing which it felt like the battle was lacking, on the defending side, was a leader. With Jon and Danaerys off on dragonback, barely five words of dialogue between them, the rest of the forces were just these scattered little groups all fighting their own battles, mostly in quiet desperation.
