The speed estimate is 73 Megabits per second Mbps, not Megabytes per second MBps.
All ISPs quote speeds in Megabits per second. 73 Mbps is very near the maximum for FTTC 80Mbps.
@LiamTeamMiniHub Is posting incorrect information.
@JohnMayer Unless you move to Virgin, it doesn't matter which supplier you use, they all use the same Openreach network with exactly the same speed governed by the laws of physics over the copper network.
Internet speed (all providers) is measured in Mb not MB. 73Mb FTTC is actually very good and you are not going to get better unless change how you receive your broadband i.e. FTTP, 5G mobile, cable etc.
As to your slow machine only receiving 8MB that is explained in my 1st point in the fact that 8MB is 64Mb, so 64 out of 73 is not bad.
The MB to Mb thing is bad but its the same with all ISPs and now its a bit late to change it, can you imagine peoples reaction to being told that their 1000Mb connection is now 125MB?
You won't need the modem any more as one is built into the Hub.