Even in it's best days, classes and factions were biased. The battle system heavily favoured melee. Promises were unfulfilled. Change was slow WHEN it happened.
This game hasn't had an upgrade in graphics for ever 10 years, and it was moderate even then.
As soon as games came out that could do all the things DAoC promised AND improved on their terrible battle system, people FLOODED out.
By the time they tried to fix things with Warhammer Online, it was too late, and people were playing and invested in other games.
DAoC is a great example of a game that could have taken over the world, but decided to dig in it's heels to make it's players accept mediocrity rather than innovate, and betted that competitors would do the same.