I expect you are correct.

The Amiga (except some early 1000s) also had a Extra Half Brite mode that has 6 bitplanes, 64 colours with the second 32 being half the brightness of the others.

https://en.wikipedia.org/wiki/Amiga_Halfbrite_mode

The extra data fetching does slow things down.

https://eab.abime.net/showthread.php?t=102990#:~:text=And%20....

The panel at the bottom looks like it uses the copper to have a different palette to the rest of the screen. That is a very common effect.

https://codetapper.com/amiga/sprite-tricks/shadow-of-the-bea...

The Amiga could display more colors than that with copper hacks though. Look at Shadow of the Beast.

Other than using copper to change palette entries at desired scanlines, Amiga 500 can display 64 colors in EHB (Extra Half Brite) mode with 6 bitplanes. Since there are only 32 palette entries, the upper 32 colors are otherwise same, but half the brightness.

And of course 4096 in HAM mode, but the mode has severe limitations and is completely impractical for textured 3D-games.