With one, very notable exception: supporting multiple simultaneous logins.What it took a Cray Supercomputer to do in 1981 your average laptop can do faster.
Modern laptops lack the data throughput capabilities.
Note: The Cray 1 was a 1-5 user machine, with 2 MB of CPU Ram and 160 MFLOPS.
A 1980's era wang mainframe supported upwards of 20 simultaneous users, with far lower processing speed, but tacking on 50 VDTs does up the tonnage somewhat.