What RPG games do you know that don't have this mechanic? I mean, if you generalize to the "you gain points after completing objective", aren't all RPG games require a player to get something upon completing certain actions?

Pillars loosely moved away from this by shifting the experience granted from combat to filling out the encyclopedia of enemies. Unsure how to feel about it but at least it's different.

Having many parallel progression systems is a simple way to feel like the player is always making some form of progress from combat but for me having many systems cheapens the feeling of progression. I much prefer few distinct power level increases than a gradual accumulating mass of them.

You mentioned money as a reward, and overall I usually find money systems tiring that are either a huge hinderance the whole game or something that becomes trivial after a short while, losing all impact.

there should be like 5 types all item shops related ofc like in those mobile games
no wonder people play those the most cause it just works

Progression through rewards is a big part of makes an RPG, IMO.

To what degree you should be rewarded for combat is another question, of course. It's an established system, it works, but it also comes with its downsides, e.g. encouraging violent solutions for every problem, turning PCs into bloodthirsty killers, because the players are eager for more rewards. The error that I've seen some RPGs (or better yet mods) commit in trying to do things differently is when they just scratch the rewards for combat while keeping everything else as traditional as before, and that does not really work. If the game still involves a lot of combat and no alternatives, but does not reward the players for beating those battles, the constant fighting will begin to feel pointless and tedious to a lot of players very soon, and they might get bored and annoyed by the design. If there are no rewards for combat, combat should be used more sparingly and/or there should be alternative ways around it and other ways to gain rewards for progression.

If your question is whether rewards have to be expressed in points and numbers, then no, in theory it should be able to come up with other ways to make the game feel rewarding and your character progress.

Also, the rewards are relative, of course. Money is only rewarding if there are enough interesting and affordable things to buy for it. Experience points are only rewarding if they cause a steady progression at a reasonable pace and the character progress is worth it (so 1/1000 XP with 1000XP allowing your character to increase their critical hit chance by 1% wouldn't feel much different to me than not getting anything at all).

I don't have an opinion on the amount of different rewards. Most RPGs I've played only reward you with XP, gold, and (loot or quest) items at max, and that's fine by me. But as with most of your questions, I have no fixed universal answer of how a game should be; it all depends on the game and how well all of its systems fit together.

I would be good with a game that only gave XP at quest completion. I've seen a couple. That removes grind incentive.

I'm OK with gold/loot post-combat being kept.

Now other AP/TP/whatever-ranks-up-your-abilities-but-not-level... That's a variable to consider. If you make it encounter-based, you can still grind-up within classes. If it's outside of it, a player may have a hard time exploring the classes/powers.

What if AP-etc were per-quest and XP were during encounters? That would be an unusual flip. Fell Seal is de facto like this, since it can be challenging to AP-up your classes without also leveling up. (AP earned is based on level difference between user and target). I think that's backwards of what I'd most commonly want. Keep level constrained, but allow development of skill set.

Tabletop RPG note: my group (and many out there! and most RPG systems) long ago went away from per-encounter XP to checkpoint level-ups (or at least milestone/quest XP if not fully to checkpoint leveling). Games that still have loot usually preserve "loot after every encounter", but some games abstract that away. Few games have a 3rd variable.

The challenge is that outside of RPGs, the reward for victory is almost always a higher difficulty (although we have games like Wing Commander to make an exception of this rule). Effectively, though, in RPGs the opposite is true. To that end, i think RPGs are fairly good for relaxation moreso than challenge, but as points are given and can improve a character, this is a fairly good difficulty control, as well. The biggest hurdle, however, is that people who are least invested due to the least skill are going to be more punished as a flip side, and thus we have a "love it or hate it" attitude towards RPGs, especially considering you effectively start an RPG at it's hardest difficulty.

It all depends on execution and the game, including experience tables and adjusted difficulty (if any). They are a traditional staple, but I also feel they're overused and would like to see more innovative progression systems.

FF8 and the 13 trilogy are great examples of innovative battle reward systems.

In 8, you have salary levels that are based on your rank and # of monsters defeated and checked to a table if it increases, decreases, or stays the same. I found it quite refreshing never having to worry about money (and EXP for that matter).

FF13 took away earning gil after earning battles in favour of drops. For the main quest, it was pretty novel because you could beat the entire game with your initial weapons and you always recovered your HP after each battle, so there wasn't really a need for money. But they hid the Treasure Hunter achievement behind raising lots of gil in the endgame, which made post-game a huge grind to complete. If they had raised the drop rates and removed the achievement, I don't have any complaints about the battle rewards.

FF13-3 reinstalled gil, put in a limited # of monsters, but removed EXP from battles in place of quests. For the EXP sidequests, I thought it was a good mechanic and as fast as grinding in battles especially after beating the game since you can always NG+ grind. I wasn't a fan of the limited monsters and money aspect because higher-tier weapons and garbs required a lot of gil farming on a limited pool of monsters that scaled on your story progress. But those are minor complaints compared to the time limit,even if it was pretty lenient and fighting more battles meant getting more EP to stop time.

Trails in the Sky FC and SC also took away money from battles, which forces the player to do sidequests and the main story to afford better equipment. If you're really paranoid, you could probably softlock yourself if spent all your money on the equipment, but have a single-digit amount of rests you can make at the inn until the next quest. Luckily, the monsters usually dropped cheap drops you can always sell so that it's not a significant issue.