This has always been a problem to be fair and some may argue that it’s part of the mmorpg genre or any other genre based on rng rewards to artificially keep content relevant, but lately I feel that we’ve reached an unsustainable point.
The main culprit here is Save the Queen content. The amount of people that clearly pay no attention and/or don’t care at all about fellow players is astonishing and, frankly, depressing. I’m not only talking about players that fail or refuse to do the content as intended (e.g. use the damned lost actions and essences, they’re there for a reason), but also people that clearly want to wait for the rest of the group to clear the content for them, which is pretty obvious in some cases (like people dying and refusing a res until the end of boss fights in castrum or dalriada). The problem is, the current design of Save the Queen content not only allows it, but it even encourages it, which is a real pity as mechanically it’s probably the best casual content the game has ever offered.

Then you have the usual clueless players that seemingly got to level cap without ever reading the tooltips of their skills, but I’ve lost faith in them at this point and I’m not going to talk about them.

Now, I know this has been discussed in this forum previously, and it’s probably me just venting here to an extent, but do people really find the current situation acceptable? Is it wrong to think that players performing terribly should be given a penalty and ideally be denied any form of reward for the content they’re running? I’ve seen people literally suiciding on the edge of boss arenas to then gleefully come collect their treasure chests after everything is over in castrum. The average player in Delubrum is doing around 20% of their ideal damage, as can be easily inferred by glancing at the aggro list when there’s not a tank with a tank stance on in your party.
We’re not talking about min-maxing or tryharding here, we’re talking about a performance gap so huge that one good player can literally outperform an entire full party.

Suggestion to the devs: expand “FATE-like” performance based rewards to most aspects of the game.

One thing Bozja did (almost) RIGHT is duels, namely the fact that you’re allowed to engage in them only if you’re “good enough”. The system is not perfect, since you’re technically eligible to participate in duels even if you do almost no damage at all and just dodge mechanics correctly, but it’s still something at least and at the end you still have to beat the boss by yourself. What I suggest however is something slightly different: take the reward system of FATEs, refine it and apply it to, well, any other combat content of the game.
At the end of an instance, you’re rewarded with a medal based on a general measure of your contribution to the party depending on damage, healing (excluding overhealing), damage mitigation and resurrection/raise casts. If you don’t pass a certain threshold, let us call it the “basic decency level”, you should be denied any kind of reward. This threshold shouldn’t be too high, in qualitative terms it should be reachable by performing a decent rotation at min ilvl while not dying too much, and reaching this minimum threshold makes you eligible for normal rewards.

Then, increase the probability of dropping rare items if you do particularly well, so that those few players carrying the whole alliance are at least awarded something for their effort. Just like FATEs, high damage and spot on healing result in better medals and each medal is associated with a multiplier that is then used to increase your reward in various forms. In the case of a huge performance disparity, reward the carriers with a special platinum badge that guarantees or significantly increases the drop rate of the rarest items in the instance (this should be a rare occurrence, hopefully, so it wouldn't make rare drops too common).

What I believe this system achieves:
1) it aligns the interests of all party members. Be an asset to your party and you get more for yourself, it’s as simple as that and it’s a fundamental rule of most group activities, including games;
2) it encourages people to gear up and not tackle content with bad gear;
3) it makes it obvious to less experienced and new players if they need to get better (if you think you’re good but you’re only getting bronze or silver medals, maybe it’s time to take a look at your job’s guide);
4) it might remove or reduce some of the toxicity and passive-aggressive behavior that can be witnessed in some aspects of the game thanks to the incentive given to the carriers.

Alternatively, if you believe similar systems have no place in ffxiv, please consider allowing full parties and pre-formed alliances to reserve an instance in large scale content such as Eureka and Save the Queen, while scaling the bosses’ hp to the number of parties in the instance.