I've restarted my quest to finally get Master Angler and the rare fish RNG doesn't seem to be worse than I remember it (it has been 8 months since I fished for that in zones with all types of water).I've noticed that myself, with holes going dry after 2-3 casts. A fresh one should have 15 or so. If a hole dries up faster it means that someone has been there and has caught a few fishes, then left. I've seen players do that, maybe people going after the achievement, getting the fish they need then going to the next type of water or zone, or simply getting bored. Currently I'm stuck in Stormhaven, with terrible RNG at the blue river fish, I've caught the green ones about a dozen times each but no sign of the blue one.