Well, for my personal experience it ultimately comes down to a slower speed being an obvious form of padding to a game's length. I played a lot of D:OS's beta, with an interest in getting a feel for various item and crafting systems.
A large amount of my playtime was waiting for my characters to reach areas I've already explored to finish quests, get to tools to craft and blacksmith, and to revisit merchants to see what goods they got on level up. Generally I'd look at another monitor / multitask during this time, as no new gameplay or content occurs during it. D:OS is obviously going to be long and content-rich, and I've really enjoyed the content I've seen. I just have little desire to plod about retreading my steps slowly and it's one of my few complaints about the game.
As far as immersion goes, is there some deep lore behind the available portals and why people are perfectly fine living next to them? Or the pyramids doing what they do? They feel like handewavey conveniences included for the player's benefit, so I don't particularly understand how walking at a normal pace is somehow poisonous to the immersion. Yippee, I can whip out the magical pyramid to port to my friend because walking there is too slow, fantastic!
It looks like things were definitely too fast before, it got overtweaked the other direction, and you're really overselling the 'problems' of a small increase. Calling people disliking the out of combat movement speed impatient and saying upsetting them is the only issue with keeping it the same is childish.
Maybe make Speed's bonus to out of combat movement more noticeable? Have +movement equipment noticeably affect out of combat movement? Let the duration of haste spells be longer out of combat? Have a trait that isn't tied to an arbitrary skill increase movement? Lots of solutions if you don't feel like a flat increase is warranted that people who like a slower pace can avoid or take once they get tired of walking through the same area repeatedly.
Anyway I disagree that the walk clickable area is at a good size, but really a run toggle solves that so the area is meaningless. I'd rather the game always assume I want to reach an area where I click as quickly as possible, unless I specify that I want to be walking. The arbitrary area of clicking creating a change of movement behavior is the issue here, when it should be at the player's discretion.
