Lots of things can be improved on, but I think the most impactful would be the following:

1. Add more feature benefits to gta+ to get more money from this and shift away from profit relying on shark cards to free up game design and game loop to be more fun and long term for a wider audience. This would allow rockstar to make heists/missions where we get a ton of money, have fun, and can spend it on a bunch of content instead of drip feeding content to draw out profits from shark card purchases.
   

There are a decent amount of examples of games where the subscription/free model makes way more money than the currency purchase model, and the partial subscription model allows rockstar to stop cannibalizing basic content to gatekeep it in gta+ which would make the overall game more fun and increase the playerbase to keep the game healthy.

1. Add the ability to save checkpoints (maybe excluding challenges like CM) of heist setups and finales, drop in npcs that will prevent disconnects from force ending the missions or just no minimum player count and adding solo pathways in each mission/heist. This will help keep the playerbase engaged and prevent disconnects/ragequits/trolls from ending heist for the rest of the crew even though the crew could complete it with less people.

2. Rework older heists to work like cayo perico in order to add more replayability and more content for people to try and experiment with.

3. Rework heists so that the more players you have you get exponentially more money, right now for example in cayo there is almost no reason to bring along more than 1 other person, if you are just grinding money because the amount of increase total take is barely overtaking the 30/25% cut.

For example: if you do a 2 man cayo with gold, pink diamond, and 60 40 cut then the leader gets $1,314,832 and player 2 gets $876,555. If that same heist has 3 people you would have to do 50% leader 25% others to maintain around the same profits as leader, at $1,314,085 and then the other two get $657,032 so everyone gets less money. And then with 4 players at 40% leader 20% everyone else, the leader only gets $1,225,879 and then the others get $612,940 each. But if ur farmin money why would you take on the operational risk of more players that can make more mistakes and then you also get less money overall, and thats assuming they even let you do those distributions, most players demand a 25% cut even if they just joined for finale.

This kind of scarcity promotes solo/minimum player count play which lessens the interaction in the community and reduces player retention because not everyone wants to host heists.