My local airport is a regional hub, though. Two terminals, both domestic and international flights. They make it work. Surely you just manage the gates in groups - at our airport, it's terminal 1 and 2, gate groups A-D - and make changes as necessary? As long as you keep the flights in the same grouping, a numbered gate change shouldn't be that big of a deal.
Probably TLDR but I'll give this a go.
Problem for example specifically at LHR T5 is you have the three terminals, A, B, C. and obviously (?) each one is segregated departures/arrivals and the two communities can never meet, not even on the transit train that links the three sub-terminals.
If you are departing T5 then you enter the system in A and if you are headed to a C gate you can train it, along with other departing passengers out to B and C....OK simple so far..you get to C and your planned gate really early.
Problems start if there is then a gate change back from C to say A......you are still a departing passenger...you cannot get the train back from C to A because travelling in that direction the train is set up, segregated and policed to ensure it's for arriving passengers..
The only way backwards through the system to return to A is to use one of the two segregated pedestrian tunnels..that's it's about a half mile plus C>A walk (which BTW it is quite pleasant and has much to recommend it over the monorail if you have time).
Hence the T5 authorities really don't like people heading off to the outer gates well ahead of schedule ...and hence the gates are not written on boarding cards or advertised on TV until about 45 minutes prior to departure, at best.
I take the point about trying to keep the flights within a group of gates to faciliate change more easily but there isn't the gate space, certainly early AM to be able to say we'll only ever gate change within A or B or C....
Other airports obviously have different issues and I know do things differently.