I think Tau is the worst matchup for Eldar honestly. It's rare to see Eldar at a significant disadvantage, but against Tau they can struggle. When fighting other factions Eldar infantry can make use of their superior range, but that isn't viable against Fire Warriors. Warp spiders are still quite good of course.

Tau just needed more FW, not sure why they went Kroot early on when FW> DR, especially when he already had Vespids & the Commander with his snares. Towards the end, the Kroot hounds could've come in handy against the Warp Spiders.

Because melee in DoW 1 is pretty bad and susceptible to kiting. Not to mention that melee units are just standing around and waiting for knocked down units to stand up instead of whacking them. People can say about DoW 2 what they want, but it has 100 times better melee than DoW 1. Also, Dark Reapers do the same kind of damage as Shees at a safe distance, further emphasized by Fleet of Foot. Shees are situationally useful in Tier 2, when they can get power swords and War shout. In tier 1 however, Shees are just throwing away resources because they just get wiped by anti-infantry weapons like snipers, big shootas, heavy bolters or Seraphim kiting.

Eldar are honestly the strongest faction if you play them right.

Susceptible to being rushed at least when I play them. I've always found Orks to be difficult to fight as tau at least until lategame but usually you can't get there. But once the fire warriors shoot halfway across the map they are ridiculous