About what you say this game is made around defending static points in fortified positions. Orks are very good attacking, csm are very good defending and lsm are good at both. While eldar main point is mobility and fast attacks. They are very bad at holding positions and breaking fortified ones, so they must cling in preventing this situations. They must destroy enemy transports and use surprise attacks (ss and sh) as a distraction in order to have any chance to win.
I would love to play in a map where you have to defend a movile objective between two points.

None of which I disagree with.

To reiterate my main thesis here: my issue is not that a co-ordinated Eldar team can annihilate an enemy force. My issue is that when I'm playing as a force getting annihilated, I have the least amount of fun if the faction annihilating me is the Eldar. And I feel the cause of this is not due to the guilds playing as Eldar doing this on purpose, but the mechanics of the game

I hate to cling to the anti-vehicle situation so much, but it's the most easily demonstrated. Picture two trukks full of Orks:
Trukk A runs into an anti-vehicle trap sprung by the Eldar. A swooping hawk hovers overhead dropping haywire grenades. A falcon tank swings around the corner, spewing lasers and dropping off a fire dragon. A dark reaper keeps watch from the gantries above to finish off the tank or stragglers as needed. At the end of the firefight, the trukk and its passengers are destroyed.
Trukk B runs into an anti-vehicle trap sprung by the LSM. A devestator pins the trukk in place with a grav-cannon. A predator tank swings around the corner, spewing shells and dropping off a melta tactical. Another devastator keeps watch from the gantries above to finish off the tank or stragglers as needed. At the end of the firefight, the trukk and its passengers are destroyed.

I feel the difference is that if you were to survey the two players, the passengers of Trukk B would report having more fun

I disagree with this example. Its never fun to ride in an ork vehicle. Damn thing goes airborne just from roadkilling an eldar and then it sort of floats/lazily crashes onto its side and a few seconds later it explodes from being on its side.

Its not that Eldar aren't fun they are a hit and run army who's tactics are get in hit you and get out before you have a chance to being your weapons to bear on a far more squishy enemy who could not stand toe to toe against you. The other two factions in EC are toe to toe fights and that's what annoys people the most.

Let me break this down, because to some extent the game was designed around the philosophy of asymmetrical balance. While it does do that, balance is still a nightmare because it's nigh impossible to find a sweet spot that keeps the majority happy.

Chaos, Loyalists, and Orks can fight the way they do because they're plenty durable. With healing bubbles, rooms packed with healing grenades, and generally hardy soldiers occupying these spaces, the other three factions can gleefully take a few hits and fight out in the open like men. This gives some leeway with tactics, allowing the more 'fun' aspects of the game to pop up in heated battles between these factions.

Eldar can't do this. They're squishy, they're specialized, and they exist both in-lore and in-game as a force that ruins your day before your day even starts. I'm talking breaking the coffee pot just before you get out of bed levels of day ruining.
They have to, because anything else gets their paper-thin taints absolutely destroyed by walking armories. Tactics that you'd normally consider cheese are the requirement for Eldar, because the game won't let them do anything else, at least not if they want to win even half the fights they do. As much as I hate hate FUCKING HATE putting up with it, it's just how the game goes.

Moral? Hate the Xeno, but hate the game EVEN FUCKING MORE.

Eldar are tryhard.
We are, on average, more experienced than the enemy team, but not really 'better'.
The reason why our games end up the way they do is because we put twice as much effort into winning.
We are doing that primarily because we aren't left with another choice but to exploit the shit out of every facet in the game.

There used to be a time when I felt bad for exploiting. For Dragons, for Haywire, for the Tempest or the Reaper.
Not recently tho. Other factions have it so bloody easy. I wish I had a fraction of their cheese, so I could just chill out for a match and still win.

I get why that sucks. Fighting a tryharding team is no fun, especially when your own team just wants to play casually and enjoy the game.
If you want to 'fix' Eldar, start by buffing us to the point where we no longer need to rely on cheap tactics, that alone will go a long way.
After that, we can talk about nerfing some of the stuff that makes those tactics possible in the first place.

But I warned you! But very few people paid attention to this... A series of endless nerfs and the passivity of the eldar community led to the fact that the eldar did not remain. Beginners are not able to resist against the SM. They are simply raped.

Horus, you cannot warn, because you yourself didn't listen to Magnus's warn about your heresy

I can tell you that playing as eldar with randoms against guildstack is a pain in the ass. Because of redeploy feature. It's impossible to cap a point when it takes 15 seconds for LSM to get half of their team from another end of the map. Even if you cap 3 points at once, they will decap, because 3-4 pointy-eared of skilled randoms =/ 3-5 LSMs of skilled clanstack.
I can assure you, that even eldar guild CANNOT WIN against LSM/CSM guild. They are at the bottom now. It's time to say that LSM players say that Eldar OP, but after playing as Eldar they say that it's impossible to play as them (yes, it takes some time to understand eldar tactics, which are OP, even if you play it as lsm or csm)
So the only way is to pray to devs so they can totally REDESIGN eldar. Because they have only two conditions - too OP and strong/too weak and overnerfed.
The only emotion that I have while I see eldar playing

Trukks are the most fun imo. Handles like a drifting buggy. The other vehicles are just boring. And you can honk!

Trying with some neutral points i have about eldar and game in general that are not too much about eldar themselves:

I'ts really difficult to really tell how op a certain faction is without a good ladder system where you could clearly see the top ten teams and see what faction they usually play.

I'ts also difficult to balance asymmetrically when there is a lack of "neutral" game modes without attackers or defenders and the entire game is based around frigging rushing points and using vehicles as lawnmowers/teleporters.

Adding said "neutral" game modes like king of the hill and simple death match might actually turn the op eldar into the up eldar if they cannot properly use some of their cheese.

Ok I'm done being neutral who the fuck thought that giving an eldar character noclip and essentially a wall hack with it with the 3rd person camera would be a good idea. Balancing shit like this is just impossible either making the character op as shit or pointless. But stuff like this could be fixed with a deployment system overhaul. Now you just spam the meta without any second thought.