I do not have a definition of RPG but here are some thoughts:
My best idea is based on an article I read about character skill vs player skill. - Action game: The result depends only on how and when the player presses buttons. You shoot at the enemy and when the cross hair is on the enemy when you press the shoot button you will hit. The enemy attacks and only when you press dodge or move at the right moment you avoid the hit. Your char might have stats (usually every game has a health bar), but if you do not push the right button in the right moment you have no chance. - RPG: You give your char the command to attack the enemy. If you hit or not depends only on your equipment, stats and positioning. Your abilities to push buttons with the right timing is meaningless as long as you somehow manage to give your char commands at all. - Action RPG: You have to press buttons to move, attack and dodge, but you also have stats, equipment and levels. So pressing the right button in the right moment is importent, but you still have no chance to beat a boss when you are a lv1 char with a wooden stick and hard fights become easier when you gain some new levels, equipment or abilities.
Usually RPGs have also: - A complex story with many different characters - There are many different NPC, some of them give you quests and you get rewards for doing them. - You grow stronger over time by gaining levels, equipment or abilities.
So BG3 is definitely a RPG, as well as almost everything else that is besed on PnP and also most JRPGs are also RPGs.
I also think that genres get more and more blurred. It all started with simple arcade games ( I think pong was the first popular electronic game, then came stuff like space invaders ) and when games became more complex it condensed into several destinct genres. While there were always games that mixed things up, now its more normal than ever before that some games do not clearly fit into one genre but instead they have many different elements from many different genres and often they add something completely new.
final words: - BG3 is definitely an RPG by any possible definition I can think of. - I do not care about the definition of RPG. I care about that I enjoy playing a game. I like both westen and eastern RPGs (BG1+2, Kingmaker / Trails of cold Steel ) and action RPG ( TW3, Fallout NV / Nier Automata ) and I definitely love totally weired stuff ( Undertale, Disco Elysium ) I also value a good story more than the game mechanics. I love PST but I never finished IWD, not because it was too hard but because I got bored when I had forgotten why I was here after killing tons of monsters. There is only one dungeon crawler I have ever finished ( a JRPG with crazy characters and lots of text for a dungeon crawler ) and I never played a rogue like because I prefer playing hand crafted content once over playing random stuff repeatedly.
Prof. Dr. Dr. Mad S. Tist
World leading expert of artificial stupidity. Because there are too many people who work on artificial intelligence already