I like where you're going with the tree so far! Keep me updated!
Do you know what time of year new buds typically appear?
Were your buds starting to swell before you did all of the work? If not, it may be slower than normal to wake up.
Here's a shot of my buds at the moment:
And here's a different one that wasn't touched:
Here's an established one in my yard:
So, my repotted one is slower to respond than the untouched containerized one, and both are slower than the established tree.
The one my thread is about is definitely behind, probably only because of the root work. I really butchered the roots so I'm not that worried. Although I repotted a lot of maples and a few are showing signs of issues; leafing out, than drying up... This does have me a little concerned that I went too hard on the root pruning with no branch pruning. So far so good with my red sprite, it's just taking its time.
When mine break dormancy, it's always a different time of year depending on my weather. Usually if we've had a cold winter, they'll wake up later, and we had a pretty mild winter We had at least a week of mid 70s here and a few days in the low 80s, most of my stuff woke up at the same time in the span of week and a half.
You left a lot more roots than me, I think yours should be fine, assuming it was healthy going into winter and hasn't experienced a hard frost since repotting.
You may have pruned off all of the conspicuous buds, do you see any at all?
If there are no visible buds, than it will probably be even longer until it wakes up. It should wake up though being a holly, they can usually throw buds on very old wood. But it might sacrifice the trunk in favor of a sucker from the base. Hollies do tend to do this, especially winterberries. In their native range, in swampy areas, the old wood tends to die back a lot and rejuvenate from their root crown.