while I was waiting for some clarification I asked the same on YT. Then I deleted the comment as I realised the forum is the right place for it - but I got a reply anyway. As it is not visible on YT I will share it here as it explains the logic behind ACES OT:
“ There certainly is - two reasons in fact. One is that to change the exposure here could adjust sampling in Corona and the amount of noise, and the second is to ensure that the ACES OT is an industry standard (which does not include any exposure compensations in it). In other words, "if you saved the raw image in Corona, loaded it in e.g. Nuke (or any other package which supports ACES workflow), set up the color science properly and displayed it via ACES pipeline, it would look nearly identical as the output you see in Corona with ACES OT enabled." - while if we added exposure compensation as an additional step in the ACES OT itself, this would no longer be true (and it would no longer be ACES OT, but "ACES OT + Exposure). Last, it is not expected that ACES OT be toggled on or off really; it is expected it is either chosen to be part of your final workflow or not, thus the Simple or Photographic exposure would be set accordingly for it either on or off and there would be no inconvenience there then. If you did have a scene that for some reason mixes both workflows, you could just save configs or set up different cameras with their own unique tone mapping stacks, and in either cases ACES OT would be enabled or disabled and appropriate exposure set to match it. Hope that helps! Tom”