I think you're on the right track with looking for a new daycare.
My own son was at the same daycare full time from 9 weeks old. It was somewhere we knew was ok as an infant, but I'd want to change as a toddler. It was all boys almost and pretty rough and tumble. He was bit pretty severely at about 10 months old. One time only so I didn't make a big deal about it. I figured that where there were toddlers and infants, at least one would be a biter. By around 14 months old, my son was biting. It continued to escalate and he was always angry after a day at daycare. By summer things were clearly not going great. The older kids were home all day from school and he was just frantic for about an hour every evening. On the weekends he was lovely and gentle and sweet. I finally lined up a new place (more expensive, but worth it). The day we set that up, I had to call in tears and ask if we could move it up a month b/c DS was formally given notice because of biting a baby (ironically it was the baby sister of the boy that bit him initially). ONE DAY at the new daycare and it was miraculous. Our old daycare was just too wild and overstimulating and put him on the defensive all the time. I had been working hard with him all summer to eliminate triggers, but I couldn't be there all day! Now, he almost never gets overstimulated to the point of aggression. Once or twice a month maybe...but not all day long like before. At the end of the first day at the new daycare, I picked him up and almost cried because I was seeing my weekend baby on a weeknight.
Just wanted to share...I've been there. And it was extremely difficult. Especially once I figured out the problem, but didn't feel like I had the means to fix it (staying home isn't an option unfortunately). Once I had a solution, but it wasn't for a few weeks, I felt like the worst parent ever for bringing him to the daycare that was causing the problem. But it was over quickly and everything is lovely now!
Just wanted to let you know our experiences. Yes, it really CAN be that dramatic of a change. And it isn't necessarilly neglect or abuse at the daycare...just the wrong environment for your child.