I think that's sorta thinking about things 'backwards'. The 'expectation' with aspects is that they are there to support the narrative, not direct world simulation. That's why it's possible to take a consequence of 'sprained ankle' when someone is shooting at you. Even though you took a consequence because of people shooting at you, the narrative you use is that you were dodging the gunfire, tripped, and sprained your ankle.
So, sorta the same thing this the jet engine. If it's some who's not that important to the story, then a single attack augmented with an aspect can probably take them out, and you throw them into the jet engine right off and they die horribly.
But what if you were fighting someone who was very important, like Darth Vader? Do you want the story to be:
Luke and Vader met up at the second death star. Then, right off, Luke threw Vader into a jet engine and the fight was over.
No, Vader only goes into the jet engine after a long and drawn out struggle.
Admittedly, the DFRG is not supposed to be fully narrativist like that, but that is why 'strong' aspects don't seem to be the fight enders you want them to be.
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Now, how to solve some of your problems with the system. You could:
1
For certain extreme aspects (like the whole place being engulfed in flames, for example) you could allow a free fire related tag against everyone in the building every turn, instead of just a single free tag. This works best in multi-zone environments, it forces people to move around, and makes creating zone borders an interesting thing to do with your action.
2
You could allow certain 'strong' aspects to give a +3 bonus, instead of a +2. (Or possibly, you could allow an appropriate declaration to make the aspect 'strong'. Since declarations are normally non-actions, this preserves the action economy.)
3
You can respond to boring re-use of aspects with a declaration like "ready for your shenanigans" if someone tries to use the same aspect over and over again against you. This effectively counters the +2 from the aspect use as they apply their free tag to their roll.
4
You can try using a more limited fate point economy, making free tags much more important. This means that any aspect used will tend to be something new, since it has to have been generated by a maneuver or declaration.