I'll admit I've never listened to any of those podcasts, but they sound like people who are quite incapable of telling two groups of people apart. I suppose the most obvious way to put it is like this:
All munchkins are optimizers, not all optimizers are munchkins
In much the same way that all murderers are humans, but not all humans are murderers. There are sadly a lot of people who tend to make general assumptions about a group of people based on the actions of a few individuals, a sad but unavoidable truth of human nature.
Am I saying that they're wrong in their assumptions? Not really. I can only guess that they're talking from their own experience, though it's possible they may have been 'corrupted' by the opinions of others in some way or another, no way to know and it's not really the point.
Instead of going on a long boring rant, I'd rather add my own comments to the points OP gives above.
1. Optimizers Don't Have Character Backgrounds - This is like saying "Players don't have character backgrounds" in that it is yet again a generalisation of a group of people, and that the definition of an optimizer varies from person to person. The only real truth I can find in this statement is something I myself am quite aware of, namely the fact that an optimizer tends to make the character sheet first, and then the actual character afterwards. For some people this is not inherently a problem, but it often results in a very mechanical and generic character, the character's personality and traits based entirely on a sheet of paper instead of an original thought from the player, and I can see why this looks bad in the eyes of others who enjoy creating their character and its concept first, and then figuring out the math afterwards.
There is also the fact that optimizers loathes to 'weaken' their character on behalf of roleplaying or adding extra depth to their character, and in the end they'll often end up with a very powerful, but personality wise boring character without any of the flaws which quite often makes characters interesting.
2. Optimizers Are Only Good at One Thing - Well, in a way it 'is' true that a lot of optimizers will make their character good at only one, or at least a few things instead of being decent in a lot of areas, this varies a lot based on character classes and concepts, but it's also true that optimizers create characters which are godly at grappling, tripping, etc.. Don't get me wrong, there's nothing inherently wrong with this, it's just that OP makes it sound like this is entirely false and they're idiots for thinking so. What I do have an issue with is that they feel the players should be punished for this, which is an entirely pointless argument, considering that DM is NOT, and I will repeat, NOT against the players, but a storyteller who is there in order to tell a story together with the players, a lot of people tend to forget this, which is quite a shame. If a player makes a character who is good in only a few areas, then the DM is supposed to create situations wherein the player can feel useful and have a good time, that's the entire point of the game after all.
3. Optimizers Are Obsessed With "Winning" D&D - Not sure what the anti-social part has to do with anything, seems more like a pointless insult than an actual argument. Regardless, I'll once again point to my above point that not all optimizers are munchkins, and munchkins are the ones who want to 'win' DnD.
Besides, there's no way to 'win' at DnD, considering that the DM is the one who decides how it all turns out.
4. Look Out For The Following (suboptimal) Signs of an Optimizer! - This is just silly and I don't feel like commenting on it.
You see, if the GM has a set narrative in mind (coupled with a rigid and reality-devoid perception of how things should work), the party needs to make a bunch of shlubs who are weak to mediocre at EVERYTHING! The challenge of everything will be set within the grasp of the players, except when the GM has chosen a party member to violate horribly and you must fail for the sake of the narrative.
When the Storyteller sees what an AWESOME role-player you are (by acting like you totally should be able to do something effectively, even though you clearly can't cash THAT check), he will dump over-WBL treasure on you, and probably at least one homebrewed artifact (probably with an annoying personality). And you shall use your ill-gotten gains to slay epic monsters, like ogres in dragon costumes! No, not dragons... You know, with spells, and flying, and things like that... Ogres in dragon outfits! Made from actual dragon scales!
Once you've harvested the dragon scales and pointedly ignored the naked, bloody ogre underneath, you point out to the Narrator that the RAW do not make dragon scale armor more awesome than what you have. Then you'll get your second homebrewed artifact! The sky is the limit... although... flying really only happens in cut scenes, because the party doesn't really handle mobile enemies particularly well.
All games are different depending on the DM, in the end all that a player can do is to make a character they think will be enjoyable to play, use said characters to interact with the world and thereafter it's up to the DM how it all turns out. Basic DnD really.
Even if an entire party only has "weak shlubs" as you put it, what's stopping that group from having fun? It's entirely up to the DM if he wants to punish the players for making such 'weak' characters, or if he wants to do the right thing and create challenges and encounters which these players can actually overcome.
To me, when the DM refers to himself as "I'm more of a Storyteller" that's a big red flag, because it usually means that he wants to narrate a story where -usually- his DMPCs are awesome and you are an inept who must be grateful because his DMPC lets them carry his shield.
I feel that you've had some very bad experiences with railroading DMs and for that I'm sorry, but in the end it's the DM's job to be the storyteller in everything but an open-world game. It's important for a DM to create an interesting story which the players can interact and have fun with, there's really nothing else to it than that.
