Ovinomancer
No flips for you!
Because rules, man. That's the fluff explanation for the extra skill increase from expertise. Sense or no sense, it is what it is. You can take it or leave it, but it's not going away just because you bring up combat. Or you can just apply the combat portion to sneak attack and their other combat abilities that they get.
You do realize that a number of class descriptions talk about mastering things and they don't get expertise, right? Wizards have a whole callout section on being scholars of magic (The Lure of Knowledge), and they don't get expertise. So, your single, selectively bolded line is as much justification as a bunch of other classes have. It's weak, and it's special pleading -- it counts for the rogue, but not anywhere else. The only reason you're even trying to make it work here is because you, for some reason, felt the need to defend [MENTION=6775031]Saelorn[/MENTION]'s argument that expertise has fixed fluff? You even admit this is barely any fluff, certainly not fixed. Again, saying my rogue is just a gifted hobbyist is sufficient for your quote and is completely supported by the lack of fluff of expertise.
Expertise is unanchored in the fiction. It the player that anchors it, if they choose to do so, with invented fluff for how they came to have this expertise. "Gods did it" is as applicable to this as "I've studied for decades under the greatest masters, and surpassed them all." Meanwhile, wizards, who have an actual entire section dedicated to pursuit of knowledge, have no mechanic support for their much more detailed fluff.
Heck, look at the prodigy feat, which grants expertise. There's nothing there, either, supporting a need for training or effort. You're just good at learnin' stuff.
Expertise is primarily a mechanic. It's not supported by fluff, or attempted to be plugged into a coherent narrative structure in the game. This is left to the individual players and DMs (as is much of 5e, to it's credit). Pointing out that this can cause oddities that have to be explained by the individual players and DMs shouldn't be this controversial. I have a feeling that there's a knee-jerk reaction to criticism of the game being taken as criticism of people who like the game, or didn't notice this oddity. It's not. It's discussion of where the potholes lie. I don't have a problem with this pothole in my play -- we steer around it or just take the bump and keep playing. But, when talking about how the game works, I don't ignore that potholes exist -- this way I'm not surprised by them.
And, this is a pretty dinky pothole.