Just personal preference. I don't dislike him, but I just don't think that there's anything spectacular about him or think anything spectacular's been done with him. He always sort of plays supporting cast to Wiccan.
It's hard when a weaker (personality-wise, or at least just interest wise) character is paired with a much stronger (or more interesting) one. So, of course, Billy overshadows Teddy. It doesn't have to stay that way but I think it's easy to think that Billy is the stronger of the two, or that they HAVE to be written as a unit, where even if it's accidental Billy will still overshadow him.
Gillen's run did no favors to Teddy either, sidelining him from the main team and having that kiss moment with Prodigy... and at the same time, it did Billy the BEST favor by elevating his status (ultimately, this was the reason they were on New Avengers when they were) and making him the demiurge, and also being the center of the run.
And while I'm thinking about it there WAS a time when writers used Billy with Teddy nowhere in sight; Sorcerer Supreme Wiccan from the Battle of the Atom reality showing up in the identically-named event and then in Sorcerer Supreme's. Writers just aren't as interested in Teddy as much as they are Billy, and as a result, his characterization suffers.