tl;dr I have data and math says you're wrong
I track all my farms. I've been doing it for a while. This is the data I have for GM:
Farm start: Dec 27th 2024 (26/30 shards)
Farm end: Jan 18th 2025
I was doing 3x100 cantina refreshes nearly every day (I try to refresh cantina energy 3x100 every single day, on rare occasions I don't have enough crystals but that's a handful of days out of the year).
254 shards over 23 days = 11 shards per day
Other recent cantina farms:
DCT: started at 29/85; 156 shards in 10 days (15.6 shards per day)
Hunter Mercenary: started at 53/85; 132 shards in 8 days (16.5 shards per day)
General Syndulla: started at 61/65; 189 shards in 11 days (17.1 shards per day)
Morgan Elsbeth: started at 9/65; 241 shards in 32 days (7.5 shards per day)
Cantina farms are less consistent and thus less predictable than hard node farms + we sometimes get bonus drop events that we can't predict (like for BB2, or most recently, Ithano). Generally speaking though, cantina farms are the fastest and if you refresh a bunch, you will get some decent drops. Sometimes RNG will just screw you over (notice the huge difference between my Morgan farm and the others).
Many other players have kept track of their farms over the years and there's never been an indication that CG are maliciously messing with drop rates. RNG just makes it seem like it sometimes, like when you're 90/100 and hit an unlucky streak of 0s for several days (it's happened to me before).