Swam drones - yes.
Loitering kamikaze drones like Harpy - yes.
UCAVs like Reaper - no.
RP/semi-autonomous/autonomous stealth drones powered by jet engines - yes.
The first two make it happen due to numbers. Enough of them can complicate the adversary's ability to track and target every one of them. There's also the matter of cost per shot, which can make it overwhelmingly in favour of the attacker. New technologies are needed to counter such a threat.
UCAVs like the Reaper have zero chance. Literally zero. They are too slow to keep up with fighter jets and too high to operate alongside helicopters, perhaps they can work at much lower altitudes, but they are not made for such a role. They lack stealth to ensure survivability. Outside surveillance and dealing with unsophisticated enemies, they are of little use in a war with even a moderately capable air defence on the enemy's side. In fact, it's among the easiest targets to kill. The limited engine capability and payload further compound the problem.
The last one is obviously gonna be the future. Even 4th gen jets mated to stealth UCAVs can deliver a similar capability as a 5th gen jet, the pairing would actually make it more capable than a standalone 5th gen.
