There are two claims:
1. A6M5 catching F6F-5 at sea level.
2. Doped AI.
Let's check... Another picture and the test mission.
https://www.mediafire.com/file/cti65tumvhcb5ib/test_F6F-5_speed.zip/fileUltrapack 3.4. Map Pacific Islands 1.
Start conditions:
Player's F6F-5 at 100 m and 490-495 km/h.
Two AI A6M5-52c at 1,500 m and 510 km/h and just 1 km on your six.
50% fuel for all. Difficulty settings: all realistic except the views/icons.
What to do: Push your throttle full forward and apply the autostab immediately after the start. Relax and watch the show.
Your F6F-5 accelerates and goes on with 513-514 km/h. Altitude slightly rising despite the autostab.
A6M5-52c dive and reach 580-584 km/h. Then they slow down and can hardly maintain 470 km/h.
F6F-5 escapes.
We can change the start conditions to give even more advantage to A6M5, of course.
Hellcat with full loadout and max fuel, low and slow and Zeke light and high.
Hellcat doing aerobatics, flaps extended. With drop tanks.
Hellcat trying to turn with Zeke at low speeds and sea level. Life is strange and everything can happen.
Anyway, I think this small test mission speaks for itself.
P.S. Yes, yes, I agree that AI can be "doped' sometimes. But in this mission, it doesn't impress and its speed matches the graphs of IL-2 Compare for Ultrapack.