I've seen the opposite problem as well- the player that refuses to optimize. They have their character and backstory perfectly in mind, and it doesn't matter to them if they can't contribute in normal ways. They will continue to play their character, their way, to the bitter end.
This can be fun. It can be engaging. It can create great moments in the game. But it can also make the player an anchor around the party's neck. There's a video on YouTube I saw once that made my eyes bleed. It was something like "Why it's rude to be bad at World of Warcraft".
The gist of it is, WoW is a team game, and if you are bad at the game, you're making the game harder for your teammates, less fun, and possibly wasting their time when they could be doing anything else. I didn't care for the insinuation, but there is a point to it.
But D&D is only partly a team game. It's also a social event. So I really can't see demanding everyone play the best possible character or always make the correct decisions. But what to do with someone who seems insistent on playing the worst possible character (and making, if not always the worst, a good number of bad decisions).
This can be the inverse of the "but I'm playing my character" argument- to which my usual reply is "yes, you are playing your character with Wis 7 as a complete and utter pain in my haldz. However, the problem with that is that you decided to make your character this way."
A year or two ago (maybe longer, time is meaningless and space is bendable) I made a post about my friend Guy (yes, really). Guy considers himself an old school role-player who hates "WotC D&D" with a passion (I keep telling him it's been 25 years, he really should let it go). He tried (and failed) to get us to play 2e (I was on board but the other players quickly developed Jacky Chan confused faces). We managed to get him to consider playing 5e, but he then instantly went against any sort of conventional wisdom when creating his character, an orphan former cutpurse who stowed away on a ship, got stranded on a desert island, and was rescued by the PC's. You may wonder what his actual chosen Background was.
Fisher, from Ghosts of Saltmarsh. See he had to fish to stay alive...
Also, he was a Ranger. Who had fairly middle of the road Strength and Dexterity, but good Con and Wisdom. And low Charisma due to a horrible scar he received on the high seas (from a guy who should know his Charisma from his Comeliness).
To try and shorten this anecdote a bit, the essential problem was everyone liked Guy. They thought his antics were entertaining. What they did not care for was how he almost got their characters TPK'd.
His response was mostly that, when dealing with a mixed group, it's up to the DM to figure out how to balance things. That's what he's done for many years as a DM.
The DM (not me) was flummoxed. "How do I do that? Do I budget encounters as if he's not there? He still gets a share of the xp for everyone else's work!"
Meanwhile, in private, Guy was complaining about how he didn't understand younger gamers, always having to min/max. Now I'm not one to care too much if someone doesn't always put their aces in their places- I have a Kobold Wizard who has higher Dex than Int, for example. But he was griping that the party's priestess had a 15 Strength despite not even owning a melee weapon, just so she could get the best AC from her half-plate.
"So what are you saying, that she should just dump strength and wear light armor?"
"She's a priestess, she should be wearing robes or something."
"On an adventure!?"
"Doesn't matter. Her faith should be her armor."
In everything, there should be balance. Snarf's OP is basically saying that. Try to match what the other players are doing. If everyone is playing Ace Rimmer "What a guy!", then things are fine. If everyone is playing Arnold Rimmer, well, second verse, same as the first.*
*even if, in both cases, you basically have to ignore CR completely. But doesn't everyone?
But if your campaign is starting to look like Gilligan meets the A-Team, it's time to have a nice chat with your players about expectations vs. reality.