is it actually worth running green just for library and friends? why not remora instead?
Yes. Sylvan Library is deceptively powerful, Ancient Grudge and Nature's Claims are insane in the right matchups, and Dragonlord Dromoka was the reason Rich won game 2 in the finals against double Dread of Night. Remora is IMO not a very good card.
why the lack of tops?
They get countered by opposing Missteps, shut off by opposing Revokers, only generally draw 1 card, and are more mana intensive over the long run.
thoughts on running library, especially in a 4 color deck? after all it is an awkward card with gush.
The deck is a control deck designed to draw a large number of cards over a prolonged game. Gush is actually great with LoA as it allows you to reactivate LoA. Again, watch game 2 of the finals.
how relevant is grudge today when shops is nonexistent online?
Shops is not nonexistent, though obviously a bit on the downswing. In any case, the card also has a place against other artifact-based Blue decks. Watch the semifinals match for an example of how vulnerable those decks are to the 2 for 1 afforded by Ancient Grudge.