G'day
@BlazenSoldier23Taking a read of your post here, there's a few things I'd like to address that may help you see things from a different point of view.
1. Starting with map sizing, while Panzerstorm appears larger than Fjell, it's about half the size. The infantry play area may be a fraction compared to Panzerstorm but the ceiling is higher, the map area is larger and more square, it also descends below the mount essentially doubling the flyable area.
Fjell is also more equivalent to an air superiority game mode map from early titles and I believe this map was put in for that very reason. Air supeririority didn't have enough dedicated players but instead of disregarding the group that was dedicated they added it to a conquest map
2. If you got shot by a 6pounder on the ground or a tank you'd expect to be instakilled, so the mossie rocking the same hardware should be expected to do the same. From what I'm reading here, it would appear as though you're falling victim to a very common problem both new and casual pilots face and that is lack of situational awareness.
As a pilot you should be aware of your surroundings both in the air and on the ground below, make sure you know not only where the enemy aircraft is but where the AAs are located so you can workout in advance if they're baiting you to one. You should be looking behind you as much as you look forward and you should be keeping a vigilant eye on the scoreboard every 10 - 15 seconds (or less depending on the situation) to see when an enemy aircraft is up.
If you fail to do this and something the size of a mossie gets behind you, the DPS they can put out is immense. In saying that Mossies are very much all-or-nothing aircraft as they have the worst turning circle in the game. There should be absolutely no reason to have one sneak up on you unless you're already engaged in a dogfight. I would highly recommend you follow my earlier points on how to be more situationally aware.
3. Respawn times on Mercury should be 90 seconds like the others, the timing is probably spot on at 90 seconds as it stops people spamming planes, which can be a detriment to the infantry below.
Also imagine you either enter a dogfight with an enemy fighter or you're a bomber trying to hold off an enemy aircraft. Say you win in either scenario but with under 20% left on health, all of a sudden the enemy you just hot down, comes back at you with full health and ammo before you can make it back to base and repair....not a good situation for anyone and this has personally happened to me on Twisted steel. No one else was going up on the enemy team and the moment I shot down this one guy he was up instantly because 2 more aircraft were ready to go. I downed him 4 times before my ammo ran out and had to get back to reload with him on my 6 the whole time fully loaded, fully healed and this repeated all game. In the end I was able to just stay closer to my spawn and keep him down again and again all game but it was relentless. Quick spawn ins would just be a nightmare.
Hopefully you can see things from another perspective and hopefully help you become a better and stronger pilot