Dragon Quest has used a point allocation system for its monster games since the DS Joker
The game that came out after Diamond and Pearl? I don't see how applies to why EVs/IVs were created/streamlined for Ruby and Sapphire from to stat exp/DVs of Gens 1 and 2. Also no the earlier GB DQM games did not have a point allocation system all monsters of the same species were exactly the same unless they were created through the weird breeding/fusion system 2 introduced, and even then if you repeated the same steps with the same species of parent monsters you'd get an exact duplicate.
main line had it in 8 on the PS2, Mario and Luigi used it in Superstar Saga on GBA
Standard RPGs aren't really the same beast those are balanced around the specific characters and as you said it's more equivalent to EVs than IVs, which are what most people were talking about. The one to three extra points in a stat per level in M&L don't really change much aside from against like the final boss there's basically no difference between 450-ish in a stat and 999 (barring HP and Stache). They're literally designed so the bonus stats don't matter. Honestly, once you've got enough Power to get past the defense of any enemy with decent-ish damage Mario and Luigi is more a game of reflexes and memorization than stats.
I can't speak for DQ8 never had any of the Playstations and I wasn't exactly looking at new 3DS games in 2017.
My experience is that they're either irrelevant and you can max out every stat and they just add extra grinding or you have to be incredibly precise or the monster's just useless and you basically have to carefully plan out where every point goes and you're basically required to essentially EV train in the main game while also probably going through (semi-)blind.
Imagine playing one of those deliberately bullshit romhacks (because that's usually the level of "balance" a lot of these games tend to have) where you have to EV train to stand a chance, but you've also put it through a randomizer to completely scramble everything's movepools, base stats, and EV yields. I've seen monsters in that take harder left turns in their stats than Hydreigon does.
Also, Point allocation has been a thing for years in Pokemon. It's called EVs, which have been well received by Competitive/PvP players, are much more comprehensible to casuals (later games having visual graphs and the general idea of "Pokemon gets better by using it against stuff good at this"), and are simple enough to influence with Vitamins or just playing that they actually CAN affect an in-game run.
Yeah, but EVs aren't manual. You can, by having the Pokémon fight specific opponents or giving it specific items, control what EVs it gets but you don't have to screw around in a menu like in lot of games it just happens.
Gamefreak's also tried removing IVs and merging them into EVs twice now, AVs were awful and Grit was worse. Because I'll remind you those are essentially what you were arguing for, and they weren't fun.