The Devil wants sacrifices, not QoL!
- Why not a charms inventory ?
Inventory management. Although D3 doesn’t have charms you have to decide if you want to have no charms, half charms, full charms, etc. in your inventory. Most of the time people play with full charms when their character is already decked out, and for PvP, and solo games. Otherwise, public games you probably don’t need as many charms in inventory because the party is probably gonna kill the monsters without the help of charms in your/their inventory anyways.
The whole reason to not have a charms inventory is for inventory management. PvP and Solo games people are going to use full charms to get the most power(PvP), or mf/life/etc.(Solo). In a public party game where people are doing Baal runs, or any kind of runs then most people are not going to use charms because the party is going to kill the monsters fairly quick without the help of charms. There is really no need of a charms inventory based on the above info, and the way people play PvP, Solo, or public runs.
So, conclusion is:
Fully decked PvP = full charms because you aren’t going to pick up items(you’re dueling)!
Solo games = full charms(mainly mf/life/etc.) so you don’t have to worry about other people ninja looting, etc.! So, it’s ok to have full charms in Solo games! Also, if you’re really decked out you can go with no charms to pick up more items that you’re gonna keep, or sell at a Vendor for more gold!
Public games = no charms. Reason is because most of the time in a party you’re going to end up killing monsters/bosses without the help of charms. This way it will give you, and the other players more space to pick up items. But, if you want charms in your inventory during public runs then it’s up to the player.
As far as stackable gems I am against it as far as D2. Yes, I play and love D3, and it has stackable gems when you collect them. D3 is a totally different style game. It is fun, and fast paced. Stackable gems do not belong in D2, though, because of how D2 is made to have items fit the tetris of the inventory/stash. Each gem is 1 square. Each wand is 2 squares. Etc., etc., the list goes on. D2R is a remaster with minor QoL, updated graphics, updated UI, enhanced Bnet 2.0 security that doesn’t affect the core gameplay of D2 that is shared loot(FFA), inventory management, tetris of how items fit, keeping items to either use for other characters/trade, low drop rates, etc.! Again, the list goes on! D2 is made to be a hard, decision making game. It’s not meant to be so easy that the game gives you every thing at your feet. You have to put in the grind, and make decisions on how you play a character and the space you’re given! 
D2 has inventory management that has you make decisions on what you keep/use in your inventory. Gotta use inventory to hold TP/ID tomes/scrolls, charms, potions, items. Compared to D3 you only have an inventory in D3 to pick up items, and usually salvage them for materials. Your inventory in D3 is usually always empty after your item salvaging, and you don’t need anything in your inventory during GR runs. The only reason to have an inventory in D3 is to pick up items, and put them in your 13 stash tabs, or salvage/sell them for materials/gold. There is no inventory management in D3 because D3 is a fun, fast paced game that doesn’t require you to have any kind of decision making for inventory management. D2 on the other hand is made around inventory management of what to keep/use. It’s not necessarily hard as in it’s a “hard game”, but rather making a choice is sometimes hard because you have to either sacrifice space to hold more charms, or sacrifice charms to hold more space. D2 is a hard game starting out because you have to grind for your items, and make trades for the items you’re missing. As you progress the game becomes a little more easy because you’re higher level, have better stats, have more points in better skills, have better items if you’ve found them yet, etc.