Lycan still had mana so he could gank as soon as he had his ult. He could also push towers early. Doom does not have that. On lvl 6 he could probably save mana while jungling so he can use his ult. But he can not use any other skills because he would be oom. Doom might be great after 15 minutes but before then he doesnt impact the game at all. 15 minutes is a long time in DotA.
Doom in lane is great though but then you have to take him instead of other farmers.