Problem with the custom mission is it doesn’t supply any rewards, and the campaign rewards are a pittance. So, it’s really reserved for the people that are done grinding, or that isn’t their goal. It’s not being gatekept per se but be prepared to really participate in some of them.
I don’t remember where it is documented about the bombers but it was talked about on the old forums a good bit. As stated earlier in the thread, ARB has been slightly tinkered with over the years without any major changes. There is a “reason” behind everything. LIke bomber gunners being reticent to say fire because players used to gunship in Sim to farm RP and thus relegated our AI brethren to low functioning status. Meanwhile airfield AAA and such have superhuman capabilities to head shot my pilot at a mile out.
Just more cases of players reacting preternaturally in response to the atrocious grind by any means they can to circumnavigate the grind. Same reason, IMO, there are so many cheaters and scummy players. The business model created them. Base stealers, kill stealers, tk’ers, cheaters. All products of the design.
Some of the user missions are tres cool though. Find a discord where people are on there squadding up and try it out to get a break from the aforementioned grind scenario. To appreciate the spirit of the game interred by bottom lined principals.