There're several internal documents on the internet showing phone carriers purposely throttle down the 4G speed, not in Australia, hopefully this won't happen here.
The document also provide prepared answers for the customer representatives when the customers report for slow network speed, like the network is undergoing some upgrade or optimization and will take some time. If you make complaint further, they would tell the customer it is due to the peak time, everyone is on the phone. If you do the third time, they could let you go to the store etc etc.
And in Australia my Telstra 4G+ speed has never go over 100 Mbps / 35 Mbps, in theory it could easily do 160~190 / 75.
And at evening peak time it is only about 40 / 2.7 Mbps
With 5G I guess you are getting something like 220 Mbps for most of the time, a little faster than a 4G+ can actually do. I'd be surprise they let you get 650Mbps
You never obtain max speed because your are sharing with others and there are physical factors like location and whats in your way affecting signal strength and losses.