Thank you very much everyone for posting evidence contradictory to my theory- I’ve been meaning to post this for a while now (either start a thread or look for an existing one).
I’ve been tracking unfarmable loot very carefully since Jan 2020 (actually earlier, but not as meticulously so I scratched the data as unreliable). Had pretty consistent drops in both 3* and 4*, posted here: [Hoarder Corner] how many AM you collect a month 😍? - #64 by Anonymous. Wish I started earlier but oh well 
.
Very shortly after this post was the Telly nerf/v30. Since then, I’ve had way less 3* and 4* AM drops- I’ll post tomorrow as I’m about to head to bed soon. I know it’s not much data, but I was very curious if others experienced the same- sounds like no.
Another factor- around the same time, I also bumped up from hitting 12-13stars to almost exclusively 14star titans. I had very consistently gotten at least a 3star unfarmable almost every titan with occasional 4stars (had a trend of at least 7 titans with unfarmables in a row once/12 in 13 days!)- on the luckier side but pretty consistent with the rest of the Hoarder Corner data. Now though, I’m lucky to get any unfarmable every third titan! Not consistent with @Guvnor’s data for Tier XIV/XV loot (Titan Loot Project - A Data Farming Project! Answering "What can/could I get from the Titan?") so again, unless they made some kind of change here or I’m on a 3-4 month long unlucky streak…