I largely agree with folks who are saying it isn't really an issue. I think most often, it really isn't...unless, as [MENTION=22779]Hussar[/MENTION] suggested, people make it an issue. I think the 5E mechanics make it far less of an issue than some prior editions.
I do have an example where this came up. This was during the time when my group had abandoned 4E and moved over to Pathfinder. This was the last time I DMed for a Pathfinder game.
I had a player who played every week. He built an Arcane Archer that he loved. The character had a good deal of versatility and utility, and was very effective with his bow in combat.
I had another player who played occasionally. Every time he played, it was with a new character. He had access to just about all the books, so the options available to him were plentiful. All of his characters were specialized in one way...he made a polearm fighter who focused on tripping his enemies, or a pure tank to have as high an AC as possible, and so on.
So the occasional player made a new character...a barbarian of some sort, and he could basically force enemies to attack him in melee through some BS feat. Character was min/maxed to the gills, multiclassed in some way that I can't recall, and was a beast in combat. A bit annoying, but we can deal.
The issue came up when, at a moment when the character was unable to rage, he found himself needing to draw his bow to try and reach his enemies.
And that's when I found out that this barbarian had a better ranges to hit than the arcane archer. And that just annoyed me. This is like the thing that he's third best at...and he's better than the arcane archer. Bonkers.
So now....what do you guys think? Should my regular player who uses the same character that he loves every session be outshines by the occasional player who just sits at home for hours and creates builds for different characters and then tries them once and discards them?
I think you missed the part where most people are saying it isn't a problem "As long as all the players do it". They are all specifically saying that a single player outshining others is a bad thing, but that min/maxing itself is not the bad thing.