I suspect the ability forcing you to sacrifice lands would be seen as a drawback, meriting the mana cost reduction
As such, a lot of deck building focuses on not just your Pokmon lineup, but also what specific tools you need to deal with a problem
In the precon I found it was mostly a finisher for when Oona, Queen of the Fae was able to stick around for several turn rotations and you had enough mana to put into her activated ability
Urza's Block was no exception to this rule, so Sigil on a flyer often equaled doom for a hapless opponent, as their best creature went home every turn
When a Town controlled by the owner of the exiled card enters, sacrifice this enchantment
This a respectable card, but when you compare it as one of the best phoenixes to something like Consecrated Sphinx as the best sphinx, its not even a competition