So it looks like the re-launch time for returning bombers is affected by your replacement rate, with the result that a Drover that's using its ship system will just perma-crash its replacement rate - reduced RR means you spend longer with your fighters re-arming, which further reduces RR, until the Drover just doesn't get fighters out at all except when it activates its ship system.
While the Drover's system definitely needed a nerf, the way this actually works out in play makes the drover basically non-functional past the first couple of bombing runs in a battle. Edit: And, critically, it means that a bomber-equipped Drover that never uses its ship system actually performs better than one that uses the system.
(Non-bomber-based Drover loadouts seem to work better - for those, the ship system's extra fighters act as a shield against losing replacement rate.)
I'd suggest either not having the replacement rate affect bomber re-launch times, or, alternatively, have bombers that are being re-armed still count as 'active' for purposes of RR decay, so you don't get cascade failure where slow re-arming times just cost you that much more replacement rate (leading to even slower re-arming times, etc.)