Marandahir
Crown-Forester (he/him)
Penalized is a strong term here.It is not only the best, but you are penalized for taking something more thematic like Sage or Acolyte.
Both of those two backgrounds boost Wisdom, one of the Monks two most important ability scores.
There is not reason the Monk can't take +2 Wis, and +1 to either Int, Con, or Cha (depending on either of these two backgrounds), and still play just as well. You do not need the +2 Dex, +1 Wis, or +2 Wis, +1 Dex to play an "optimal" Monk. Whether Standard Array or Point Buy, you're not going to have a character that is 18/16/10/10/10/10. There's always a reason to have an "off-brand" ability score boost, even for a MAD class like Monk, for the purpose of secondary skill or tool usage.
And that's not even considering that Sage is Int/Con/Wis, meaning you can put the extra +1 into Con, which is nearly as important to Monks as Dex and Wis (as it is for nearly EVERY character who either (1) engages in combat or (2) has reason to maintain concentration).
So from even a CharOps perspective, sure, Sailor might be Gold and Sage might be Sky Blue, and Acolyte might be Blue, but they're still all recommended options mechanically and that's even before we get into the idea that Backgrounds are not there to be CharOp tools so much as story hooks that help show why you're different at level 1 from every other member of your species and/or class.