Syndra is like a fully farmed veigar
except at all points of the game. while having more reliable skillshots and a nuke that doesn't require enemies to be low to work.
I don't really see why would I pick veigar ever with syndra as is lol. I don't think veigar is weak or anything syndra is just a better version I mean she is strong early and she doesn't fall off at all.
her base damage numbers make up for the massive amounts of ap veigar has as the game goes.