I think the current situation it's the total opposite of what you're saying: the parsers didn't make the community more toxic or less casual friendly, it's that FFXIV is already toxic and less casual friendly than people admit, thinking this is their safe haven of sweetness and sunshine UNTIL something threatens this lie.
Hell, I get bashed for disliking the main story, and God forbids you for having a different opinion about it! That's toxicity in my book and while it's a rather harmless bashing (I have enough jrpgs under my belt to know when I like a story or not), I'm fairly sure I don't get bashed for disliking stories in other games. See the problem?
This leads to another thing you mentioned in the same post
Let me ask you this: why was vanilla wow - or any old school MMORPG for that matter - so loved despite being utterly unbalanced? The teamplay and the NEED to work together with other people: you had group quests, you had dungeon groups that actively looked for people in cities, some classes were more useful than others and so forth. It was a living world because people WORKED with each other, they PLAYED with others, and most importantly TALKED with one other.
Now look at FFXIV: everything is locked behind a SOLO main quest that you cannot - YOU CANNOT - tag with others (look at SWTOR if you start bragging lore BS). You can make up groups but it's 1000 times faster and easier (especially as a tank and healer) to use the duty finder: you even get bonus rewards if you solo queue. There are no group quests in the entire game: only group content in the world is fates, which don't even really incite teamplay and people group up only to reach gold medal easier. Same thing for hunts as you cannot get full credit alone (and yes tried doing one hunt alone, from 100% to 0%, it didn't give me full credit). Even dailies can't be done with others since they're randomized for each player. Free Companies have little meaning to group play as well because their buffs are very weak and easy to ignore and once again, everything can be done solo, even raids, and if you need to group with others you usually prefer a linkshell, because you can join 8 at once and never commit in any of them.
Only people who are at disadvantage are the DPS, which is the only one who requires people to play with and as I level one myself, it can be annoying to wait 30 minutes...but still better than go to a city, spam "LFG tank and healer" on a general chat, and then wait more than hour for said people and run over to the dungeon and enter manually. And yes I did that and it was a pain, but satisfying nonetheless and people talked more than they do now!
TL;DR: Parsers won't make the game more toxic, because the game has always been about solo improvement and egotistical people - hence, toxic - and there are very little incentives to do premade and socialize (i can probably do omega with pugs and once I learn the fights, I can join any with ease)
Add more incentives, more rewards and more bonuses for grouping up and people will stop aiming at each other's throat and parsers will stop being this evil spawn that everyone is afraid of.