Some other game mechanic must take place in order to convey character development and differentiate player's experience. If characters' stats are static and there's no way other way to express the character's identity and beliefs (say, choosing between Paragon and Renegage in Mass Effect - just better), then its not a RPG. If there's a lot of combat, it becomes a Action or a Strategy game. Otherwise it's likely a Adventure (I mean focused on Exploration) game.
I express my identity via loot gathering and equipment customization, and which quests I choose to complete. M:
Though half of the post is satire, I actually believe that 'roleplaying' is inherent to video games in general. But also that a game that focuses on roleplaying must differ itself from a game that focuses on exploration and simply adventuring - meaning that a RPG 'filters' character concepts through its game mechanics, denying many and confirming one. So focusing on that last part of your statement - 'which quests I
choose to complete' - I'd say that a game that simply offers you a lot of content without 'forcing' you to choose a single path amongst many is more about exploration, as opposed to roleplaying.
In short, Skyrim is a 'Adventure' game in the sense that not only there's a lot of exploration, Skyrim's story is about a character that can effectively be the awesomest man in the land. That's what the game mechanics tell you. And as far as the mechanics care, Dragonborn can be every character concept at once. You can certainly roleplay or even larp one concept over others,
choosing not to wear heavy armour because you're a mage etc, but the game mechanics never conditioned that behavior.
Similarly, in a Strategy or Action game, what differs player experiences is their ability - which matters more than the character that they are playing, as in Action games, or the 'character' of their (in a broad sense) 'nation', as in Strategy games. Its not like Action or Strategy games can't allow for roleplaying, quite the contrary, or even that a RPG can't be a little about the player's ability (be it decision making or dexterity).
But rather that a Pure Action/Strategy game is about Player Skill, a Pure RPG is about Character Development - hybrids have each of these as their respective focus, submitting the other(s). Same thing with 'Adventure' games and Exploration.
So instead of defining RPGs in reaction to what we've seen in the last few years (IT HAS STATS, ITS RPG), I try to define RPGs in a way that subverts that. Every game can have roleplaying elements, but not every game puts defining characters above everything else. Choosing better shooting talents in <Shooter with RPG elements> does not define your character because player skill is still above those RPG elements.