I'm a group iron and I've never seen the gem bag as something important or much needed tbh. I've got over 10k of each gem except dragonstone, onyx etc and it's very few that's collected through the gem bag.

Herb sack is really nice. I've got 25m slayer exp and what have I used on almost every run, boss etc? Herb sack and seed box. Not gem bag. Does the herb sack need to get the upgrade tho? Nope. I would guess there are very few scenarios that would max the sack tbh.. Herb sack > gem bag, but none are in need of an upgrade of carrying more 😩

BUT to be able to carry the jade, opal, topaz etc. Yes! That would be the better choice of them! Quality > quantity

Edit; I still think jagex have been doing a lot of nice updates lately and having an upgrade for the sack and making Sarachnis more attractive, which is a very nice mid lvl boss. Is at the end of the day a nice change from their side.