They've certainly reduced effective inventory capacity, but I'm not convinced it's a bad thing.
Prior to these changes, so long as my backpack was blue or better, I felt I could comfortably carry enough ammo & heals to never worry about running out.
Conversely, the old white backpack forced serious compromise (either carrying only 1 stack of medkits [no syringes], no grenades, or a single ammo stack for an ammo-efficient weapon [PK/Wingman/Scout]).
After the change, I've been caught out several times with insufficient heals or insufficient ammo, or both.
Moreover the overall reduced capacities has made resource depletion of the enemy a viable combat strategy, which has given a much needed buff to the usefulness of snipers.
So I guess I support the new backpacks, as it's done enough to significantly disrupt the meta.
That said I still think the ammo efficiency of both the Wingman, PK, and to a lesser extent, the Scout, make them too good, especially as they sacrifice no combat effectiveness for their superior combat endurance.
Additionally I think snipers, while much improved by the meta shift that this inventory change has caused, are still rather ammo starved because of their dedicated ammo type & much smaller stack size. If their primary use case is intended to be the winning of resource depletion battles, then they need ammo stacks large enough to achieve this.
As-is, a Wingman or Scout that misses half its shots will still deal roughly the same damage per ammo stack as a sniper that hits with every round.
That can't be right.