The Hub4's wifi provision is 802.11ac (or WiFi 5), whereas the 5 can use the newer 802.11.ax (WiFi 6) provision.
If you look at the specs for both WiFi 5 and your iPhone model, the theoretical maximum speed it can ever get over WiFi is 866 Mb/s - but that's the 'link speed', not necessarily the speed it can actually transmit data at, think of it like the 70 MPH speed limit on a motorway, if you never break the law then that's the fastest you can ever go, but it doesn't mean that you can do that speed, between junctions 6 and 10 on the M25, at 10am on a Monday!
The WiFi is battling with all the other users around you (WiFi signals are no respecter of walls or property boundaries), and frankly, the technical way that WiFi works means that regardless of what the link speed might be, the practical data transfer rate can be sometimes a third or less of that.
Bottom line - your 450 or so Mb/s really isn't that bad and certainly isn't an indicator that anything is actually wrong.
Now I know that some people will read this and feel 'cheated', 'VM sold me a package of gigabit speed and it isn't possible to actually get that, why should I be expected to know all the intricacies of WiFi technologies and communications protocols?' And I do have a degree of sympathy with that view, except VM certainly aren't alone in this, WiFi absolutely CANNOT be guaranteed to any degree of certainty, which is why, if you carefully read the terms of service, EVERY provider will only talk about hard wired, ethernet connections.
Now in theory, a Hub 5 'may' improve things, I say 'may' because although your phone is certainly capable of using the faster WiFi 6 standard, there are still many external factors that can reduce the effective throughput speed.
