Droplets are not affected by level penalty no matter how high you level, only mesos and EXP are affected.
Our rates are nerfed on both of these things when we're working on legitimate activities such as dailies and weeklies, or just farming symbols/droplets/etc. If this is all "current content" why should we be punished for having leveled?
However it is important to highlight as you did that droplet rates aren't affected.
The main issue here is that byebye is overpowered. You should WANT to continue leveling and be getting better rates for it. The whole meso progression in reboot is a mess and will probably never be sorted out in GMS.
I do agree with the idea that being punished for leveling is horrible game design though. Specifically for players who, for example, want to continue farming in lower maps for droplets or dailies and get massively reduced or 0 mesos, and reduced exp because they're over-leveled for the content.
They should bring back the concept of a top level cap for level based reductions, it used to be at 180. In today's maple it could be at 230.