This isnt a flaw with Eureka anyone whos been playing MMOs for longer than six months recognizes this behavior its not an inherent problem with the content it's a problem with people only wanting the best groups to get done the fastest, I'm max elemental level with several relics and honestly you can find a party you just have to be willing to look, sure it'll take sometime it'll happen but it will.
I'm really struggling to understand how it's SE's fault people cant get parties, it isn't, all SE can do is add incentives to take lower levelled players but thats not SE's responsibility its the players to stop being selfish theres even ways around just spamming shout chat 'til you get an invite.
You could ask any FCs/LSs you're a part of or put up a PF beforehand to find players around your level to go with there's plenty trust me. This community needs to be stop being so determined to hate this content and actually put some effort in to make it work for them, because its sure as kupo better than another monotonous tome grind.