For instance, the Borg will 'adapt' to phasers and create shields, but you can still shoot them with bullets or stab them.
In their inaugural episode, they easily adapted to photon torpedoes without even having to take damage from an initial shot.
As for bullets, those worked once. Everything
works once against the Borg (except photon torpedoes, which don't work even once). There's no indication the old aceton assimilators would have been equally flexible in their response...
the thrusters Picard activated worked like a charm and moved the ship in the desired direction
Actually, they didn't - the episode was quite confusing on that issue.
Anything powerful enough to make the ship move would have been countered by the assimilators. But LaForge figured out that doing an extremely quick burst with the impulse engines
would be both powerful enough to get the ship moving and
unnoticeable enough to avoid a countermove from the assimilators.
Only after the impulse engines had kicked the ship into motion did the thrusters come into play. They were barely strong enough to slightly adjust the course of the ship, and their sustained use would have attracted an assimilator attack (plus, accelerating on thrusters would have taken too long and everybody would have died from the slow but ongoing radiation attack). But brief bursts again avoided assimilator attention and allowed the ship to dodge those rocks that got in the way.
We never got a scene in any of the Trek shows or movies where thrusters would have been sufficient to get the ship from A to B. They can get the ship moving at a crawling pace, such as when piloting out of a spacedock. But if that's the best they can do, they would have to operate for months if not years to get the ship to another planet, through an asteroid belt, or whatnot.
Those thruster scenes do have some built-in silliness, to be sure. Sometimes a thruster creates a bright flame, sometimes not. And when going around the big rock, Picard supposedly fires thrusters that get the ship spinning ("starboard aft"), which shouldn't alter the actual trajectory
at all - the ship would still move straight ahead (albeit spinning) and would crash into the asteroid. But perhaps the dialogue is just slightly inaccurate, or we miss key phrases because of the cuts in the action - and perhaps Picard has a valid reason for spinning the ship, as this would bring some "tidal" forces into play to further affect the way the ship's CoG is moving.