Mac mini ethernet speeds not gigabit?
Mac minis ship with 5400 RPM spinning hard drives. Even if you’re using a Fusion Drive configuration, its solid state portion is likely taken up by more-frequently accessed files.

So assuming your downloaded data gets written to some temporary file, your benchmark is running off the mechanical drive. Add to that the overhead of recording logs to a separate database, which will further decrease your storage performance.

On the other hand, Apple laptops all ship with SSDs. An SSD should easily keep up with a Gbps connection.

The most probable scenario is your Mac mini is being bottlenecked by its hard drive.