My first suggestion would actually be: "extreme" people in here than in FFXIV itself

Your're not wrong about the vitriol on these site. At times I wonder if some people literally do nothing but post about how terrible everything is (some, I'm pretty sure, actually do), but there are also quite a few truly knowledgeable about generous posters, as well. Take the vitriol with a grain of salt since there is often a small bit of truth in it, but don't treat every criticism as a personal attack. That's my two cents on that topic. As for your questions:

1) I would gladly take a safe, flexible player over anyone else in my party. It doesn't matter how much you've memorized the perfect rotation or fight if you can't adapt when a mistake happens. Things go wrong, and sometimes it's no one's fault in particular. That said, I'm not encouraging players to not know their class (please, BLMs, use more than Blizz 1 and Fire 1!) but rather encouraging people to not bottleneck themselves into one playstyle of having the perfect rotation 100% of the time and damn everything else. No class can do anything if they're dead, after all.

2) It depends. There are people who won't take less than perfection and others who won't care so long as you have a general understanding and are adequately geared, and gearing to i200 or i210 isn't too difficult anyway. Beyond that, if your friends play well (not perfectly, mind you) then most people won't even say anything about their gear. Just let them know that if they hop into EX content, check the minimum item level requirement in the duty finder for it. I'd suggest they try to get a few levels higher than the minimum unless they feel very confident in their abilities. And don't join a farm group if they're new--that never ends well for anyone.

3) Practice, practice, practice! There's no real way to introduce them to higher level content without, well, dropping them in. This game has a lot of entry level content and high level content, but is sorely lacking in mid level content. I'd have them try Void Ark or Bismark EX if they want to experience 24-man raids and EX Primals in HW, if only because they're more populated. After those, try out Gordias and Midas normal. Keep them away from Midas Savage unless they really want to get their feet wet.

4) Well, you kinda said it youself: "arguably bad developer decisions". I've heard people blame other players and others call for Yoshi-P's job. Frankly, they're both wrong, but that's not quite the point. We tend to blame the playerbase because the developers react directly to how we're playing the content they give us. For example, Midas Savage clear rates are VERY low compared to their expectations. So they're making the Creator Savage easier on us in 3.4. However, the higher difficulty of Alexander Savage was, itself, a response to people saying Coil was too easy!

Whether we like it or not, the developers want as many people as possible to experience as much content as possible in this game. Yes, they'll make some difficult fights, and yes they'll also nerf the hell out of earlier content, but that's all to help people experience the game. Whether you agree with that or not is up to you--far be it for me to judge--but regardless it comes down to if you want a game where only the top 25% play, or one where everyone can have a shot.

I hope I was at least somewhat coherent with my answers. Just keep helping your friends out and don't let them be afraid to try new things. I had a few people in my FC be terrified of Coil and EX Primals back in 2.0, and now they do nothing but bird farms for the HW EX Primals!