Nope, not "unfashionable"
Because if I were "fashionable", I would like Hadyn/Kaden/Aiden :P Maybe it's the "corn" sound that I dislike in Cornelius, or maybe the "kneel" sound. I like a lot names ending in -us, but just don't care for the sound of this one. It sounds cumbersome to my ears.
I think of Silas as being completely untrendy. I've never known anyone named Silas, and certainly not a child. I'm shocked that Silas is increasing in popularity, I hadn't heard it anywhere but by reading the New Testament. I swear everyone steals my ideas before I can use them. I wanted to make a St. Paddy's day t-shirt that said, "Don't kiss me, I'm not Irish," but someone beat me to that too. I didn't know this site had those popularity charts, though. Thanks for posting it.
But I like what I like because I like it, not because it's fashionable, but because it suits me and my husband. That said, I have taken names off my list when it's had an obvious increase on the social security list or if a celebrity uses it. We wouldn't use a name we don't like (like Mephibosheth) solely because it's unfashionable and uncommon. But we will reject a name that we do like if there are hints that it may be becoming a trend.