I'm pretty good at fitting stuff in my stash. Sometimes I counsel my friends over a discord stream so they can fit the juicy loot into their tiny normal edition stashes. This new change though is a load of horseshit. One of the easiest ways to transfer items within the stash is to temporarily put a case, a weapon case, item case, or junk box and scroll around to drag items to it. Now, that isn't possible even in the hideout because cases don't fit in bags anymore. Instead, you either have to load up your PMC's inventory from one area and then scroll down to the target area for the items and drag them over, which takes ages.
Honestly, besides the MBSS items case exploit, cases in backpacks were never a problem. People who went in with cases were super chads, with risk/reward at maximum. If they die, its 1300000 rubles gone at the minimum. That's fine. With the new weight system, this practice all but went extinct since you can't even walk with a full case.
The only real effect on the whole playerbase is that stash managing has gotten slower.