In days of yore, the term "RPG" came with it a very specific image. Isometric, D&D rule inspired combat, traditionally fantasy, dense statistics, rows of hotkeys holding special powers, heaps and heaps of text about characters, lore, and quests.
This was during the late 90s and early 2000s. Even innovators like Elder Scrolls II: Daggerfall or Ultima Underworld, don't confuse themselves with other first-person games of the time like Wolfenstein, DOOM, or Duke Nukem. They're heavy in random damage numbers, looting, and dense customization of your character.
However, even during this time, things started to change. System Shock & Deus Ex were the games that started to broaden the definition, and bring with it new terminology to distinguish itself from the likes of Baldur's Gate, Icewind Dale, and Planescape Torment. System Shock & Deus Ex, while considered many a role playing game this day, were also dubbed "immersive sims" for their environmental interactions that traditional RPGs didn't feature.
The next wave came with the original Xbox's heavy hitters, Elder Scrolls III: Morrowind, and Knights of the Old Republic. Retaining decisions, dialogue choices, and customization, but being far more restrictive when compared to games of old, in exchange for a world with much higher fidelity. These were still called RPGs, but the trajectory was starting to become clear. These games were no longer attempting to emulate the D&D mindset of creating a character from scratch, and dice rolling your way through encounters. They were about giving you a large variety of tools and behaviors you could invest in.
When this really started to change however was the 7th generation. Bioware & Bethesda envied highly population action games and were starting to make efforts to extend their games beyond the RPG crowd. Oblivion made its combat far more palatable to general audiences, but the one that picked up attention was Mass Effect. To general crowds, it looked like a Shooter, and it... kind of was?
While I love Mass Effect 1, it did cause a divide in crowds. Many RPG fans weren't satisfied as all of their variety in combat suddenly had the rules of a 3rd Person Shooter rather than D&D, but the game lacked many refinements that make 3rd person shooters enjoyable.
The solution decided then was to push the shooter aspect even more than before, and with Mass Effect 2's immense critical acclaim and high-sales, there was no going back for these studios, even with the game being questioned as being called an RPG at all.
What didn't help matters is by this time, many shooters and actions games started to implement RPG elements, the most obvious of which, was Borderlands, with its character builds, gun variants, and leveling system. Call of Duty 4 was also the big game changer.
Since then, the term RPG has gone into complete chaos with so much discussion being spent on determining whether or not a game is an RPG, while so many people can't decide what an RPG is. Some believe it's about character customization, some about combat choices, some about narrative choices.
It's a complete mess, and I doubt will ever get sorted as this genre-mixing's only continued further. Multiplayer shooters like Paladins have players weighing over character builds, stat increases, and ability management, like an RPG, but it's not called an RPG.
Personally, what I find tiring about this conversation is often at times, it doesn't seem to even determine a game's quality. All RPGs are an illusion of choice to some degree, games in general is all about magic tricks, so to hold decision making as the holy grail of an RPG is often misguided. The game could have the most decisions of any game ever, and still have uninteresting characters, bad combat, and ugly presentation.
The best that can be done is to clarify what a particular RPG's focus is. If it's an isometric game to allow developers more time on crafting more flexible decisions, then that's just as understandable as a big budget first person RPG focusing on the presentation of its fewer choices.