How would you rate the difficulty of each mainline game from the perspective of a brand new player?

I’ve been playing Pokemon persistently since Red and Blue, so needless to say I am a very experienced player. My fiance has very recently begun playing Pokemon Let’s Go after a coworker piqued his interest toward it (he mentioned wanting to get started, they said it was a good entry point). I’m really excited at the prospect that he might take an interest in the series as a whole.

He has had basically zero experience with Pokemon in general outside of entertaining me yakking about it before this, and is not too much of a gamer overall. He seems to be enjoying this game a lot so far! He just conquered Rock Tunnel, and I think there’s a decent chance he’ll want to move on to something more challenging after finishing it.

So for that reason I ask from the perspective of somebody very new to the franchise: how would you order mainline Pokemon games in terms of difficulty? I have some vague ideas myself, but would be interested to hear some thoughts from the community at large. I am able to arrange for him to play basically any Pokemon game that exists, so accessibility to the game itself is a nonissue.

I think my personal difficulty ranking would be something like this from easiest to hardest:

Let’s Go Sword Shield Red/Blue/Yellow XY Gold/Silver/Crystal/HGSS RSE/FrLg DPPt SV Sun/Moon/USUM Legends Arceus BW/B2W2

Thanks in advance!