Nope, it's definitely not because if I synchronize it over the clear net, it's super fast. But synchronizing it over the hidden service is not. So that tells me it's not a CPU issue. It's definitely bandwidth.
Discussion
Latest blocks are “a lot heavier” because not all nodes online have synchronized that blocks. So you will have a lower number of sources. Isn’t this the point?
The point was that it takes a lot longer to synchronize blocks using a hidden service than it does over the clear net. I knew it would take longer, but I did not realize how much longer it would take.