6" from the ground? Is that what you were told to do? I haven't read that they need to be cut back at all. Nevermind so severely. My annabelle is about 4 years in the ground at my home. I will try to post a a link to a photo. Try leaving it be next year would be my advice.
Jm

Here is a link that might be useful: HGTV

Thank you for the reply. That's interesting, the local nursery said it grows on new wood and trimming it low to the ground was very common for large blooms. The question is why is it not growing fast?

Maybe the roots got damaged when you moved it and need more time to become established. You are right about the new wood. I remember now... it was recommended to leave the dead wood to support the heavily flowered branches so you did no damage in the severe pruning. I also think you were right to give it more sun. I have 2 and the one that gets more sun does better. I'd give it another year.
Jm

I have 2 and I never prune them and they are currently covered in huge white balls. All of them are in complete dappled shade. I place a wire cage about 18" tall around them to help support the blooms

All I prune is obviously dead wood. Other than that, I let Annabelle do her own thing--give her some extra water during really hot, dry weather. That's about it--and she goes crazy producing big white snowballs.

Some sun is good for Annabelle, but mine are protected from the sun during the hottest parts of the day.

Kate

I never prune mine and it does seem to help with the flopping==dont prune it for a year or so== if it was 4 feet tall when you planted it you cut too much--leave it alone for several seasons and you will be pleased.

Annabelle dies to the grown in zone 5 without fail. Pruning the dead wood (which involves the entire plant) to the ground never hurt mine. However, interesting idea to leave the dead stalks to hold up the new ones. I'm going to try that next year. It took mine a couple or three years to get established. I've heard people say annabelle tolerates more shade than other hydrangeas but more sun would get it established better. Mine was getting 2-3 hours sun. It now spreads wider every year.