It is a normal name, and it was an immature reaction, but that kid is 100% going to get bullied for being named Deborah. Speaking as someone with an uncommon name, chances are high that the kid will hate the name and resent their parents for it for at least a large part of their childhood. It took me a long time to 'grow into' my name, and I was more able to do so because of it's cultural significance for me. If there's no tie to the name Deborah it'll likely be hard for the kid to grow to like the name and the fact that it's such an 'old lady' name will make it much worse.

OP was a jerk but people should think more carefully before saddling their kids with ugly/old fashioned/otherwise unfavorable names and I don't think it's unreasonable for people to have that conversation with expectant parents where appropriate (like if it's your best friend or a sibling about to name their kid something awful).