Both signing and speech feel halfway, and neither seems to be growing.

There's no need to "pick just one." Keep using both. If signs or gestures are easier for your child to use, we recommend the family actively use new gestures too, to grow the vocabulary they can express. Having more means of expression isn't an obstacle to speech, it's a foundation for it (research has repeatedly shown that using signs doesn't delay spoken language). If they seem to like letters, showing fingerspelling and letters for the first initials of friends' names is also a good approach.