FBW A380 is not compatible with MSFS2024, so how you can compare it?
First: it was a test to see how it does in 2024, as it performs like ■■■■ in 2020.
Secondly: it works in 2024.
I don’t understand your story and it is simply not true!
The FBW A380 works great in MSFS2020, but both versions Stable and Development don’t work in MSFS2024. So you can’t do a comparison test.
It’s pretty pathetic indeed. I downressed myself down to 1048p. I have a 3080 Ti with 16GB of VRAM. When I’m in a really saturated area like Chicago, it maxes out my VRAM but doesn’t seem to exceed it and trash the performance by going shared. However, my GPU runs at maybe 50-60%. In fact, this thing isn’t using the full potential of either my CPU or GPU. I’m still lucky to get maybe 20-25 fps on average. (Now, this is measured through the XBox Windows+G thing because I’ve never gotten the developer mode to actually work in MSFS2024.)
Now, if it was maxing out my GPU, I’d understand and turn down some graphics settings. But it isn’t.
One thing I can give them from the last update is that the intro video isn’t running my NVIDIA GPU at 50% and still managing to overheat the thing.
Honestly, I don’t know what is going on with their coding here.
Im not going to argue with you.
If you have not been under a rock, there are several streamers who have showed the 380 in 2024.
This is 2024; 70fps. 2020 I have 25fps…
What i mean is that FBW have said, that all there aircraft not yet been ported to the MSFS 2024 SDK and therefore they are not compatible with the new sim.
Basic systems work and you get him in the air, but comparison is only possible when FBW has ported there aircraft to the MSFS2024 SDK.
They have still a lot of work to do, so it will take a few months and then we really can compare.
You can compare anything with an everyday compare & contrast chart. 
Apples are:
- mostly round, but with dimples and bumps
- thin skin, can bite through it; often red or green
- crisp sweet flesh, taste from sweet to sour depending on variety
Oranges are:
- much rounder
- thick skin, remove before eating; bright orange outside with white inside
- flesh of little juicy pips, absolutely delicious
When the FBW A380 gets reworked to use the new parts / LOD system it ought to run faster in theory, and that’s something you can compare in the future against the version available today.
I did two flights without setup the flight with A380 from EHAM to EHRD.
To get same values MSFS2024 has lower graphic settings then MSFS2020.
Time, weather, altitude, speed are the same.
Fps - 60/57
Fps - 60/57
Fps - 108/73
Fps - 60/57
Fps - 51/49
Fps - 60/56
Scenery Rotterdam is more dense and crispy in MSFS2020
I don’t understand your story and it is simply not true! 
EGGW, the updated version from iniBuilds. It was a slow degradation in FPS all the way throughout the flight.
The A320 V2 from inibuild has the same performance in both sims (2020 and 2024) on my rig.
I think that it is not always the aircraft, but most of the time the sim who is responsible for the drop of fps.
Maybe in your case it are a few extra inserted calculations in the updated version who are responsible for the drop in fps.
Yep, the same for me. Same aircraft, same route same everything! 15fps n 2024 and 40fps in 2020. 2020 has still got all the bells & whistles and I still feel it is more realistic than 2024. With each update to 24 I come back to see if things have improved, if they have not, then it’s back to 2020. I was hoping that update 2 would be the turning point, unfortunately it was not.
Oddly I’ve had the opposite happen. I currently have both 2020 and 2024 installed, and on a 4070ti I’ll get lower FPS in 2020 in identical scenarios, only because MSFS 2020 will not fully utilize my GPU, it stays around 50% - 75% usage and will never reach 100%.
However in 2024, my GPU gets fully utilized and results in higher FPS. The only problem with 2024 though is VRAM usage.