Like with railways (where we are saddled with some stations that would never be built nowadays, but that's what some Victorian entrepreneur thought would be a good idea), our "cities" are a mess.
The Industrial Revolution completely changed the map, switching focus from "places with big religious buildings" to "places with big factories", so we've got this awkward combination of "places that used to be important when Monks and Bishops ruled the land" and "places that are fairly important in the modern era but the Mills/ Steelworks/ Docks didn't have an adjacent State Approved cathedral"- which means trying to pin down a definition is a bit like nailing down jelly.
We've also got the problem that local Government boundaries can artificially affect how big a place looks - Bradford is large because it's metropolitan boundaries extend all the way to Keighley/ Ilkley but Nottingham doesn't even get to count the Forest ground in West Bridgeford and the hundreds of thousands of people in the Gateshead area on south bank of the Tyne were in a whole other county to Newcastle - so "population" isn't always a great way to define things since there are some large populations in places that don't "feel" big (Walsall has around a quarter of a million people, but I don't think anyone would claim that was worthy of a city?).
So is it about the biggest places, is it about the most important place in the region (which isn't necessarily the same as the biggest places), is it about the most important religious buildings?
Instinctively I don't like the idea of cities in close proximity - e.g. Salford and Manchester - a city feels like it should be more of a "regional centre" (but then we are a messy country, and that strict definition would mean removing city status from places like Bradford, which wouldn't go down well!)
But I'd like city status to mean something, to be more exclusive - whereas some of the places recently awarded or suggested feel very tokenistic
Hahahaha, forgive me... but it doesn't surprise me you'd want to take it away from smaller places!
Haha

- guilty!
But there's a question about what a city is - people here seem to at cross-purposes about what criteria we are looking for - is a city determined by size or by things like Church of England cathedrals/ post offices/ history?
We've got this messy combination of "places that would be insignificant if they hadn't had a major religious building located there" and also "large places that didn't have a cathedral" (e.g. Sunderland's application around thirty years ago - suggestions for places like Milton Keynes)
Maybe we should have something like a "Royal Burgh" status for the kind of St Asaph places that would never be on the radar were it not for some medieval architecture (for the state approved religion) and keep the "city" status for actual large conurbations?
Sheffield’s main post office is in Wilko’s!
True, not even worth of being on the Ground Floor either
Still doesn't pass the smell test to call Doncaster 'just a Northern provincial town'! It's derisory
I live nearby - I like the place - but I don't see what is so derisory - Doncaster is "Northern", Doncaster is "provincial", Doncaster is a town
I'm not knocking it but if Doncaster is enough to be a city then we probably need to double the number of cities in the UK since there are lots of similar places (in which case "city" stops meaning anything). Then again, Wakefield doesn't feel like a "city" either, yet did qualify.
Bournemouth & Poole could become 1 city, a bit like Brighton & Hove is treated like one.
Mind you, it would lead to Poole gaining the word Actually to supplement it.
The Bournemouth conurbation seems to be an urban area of a size fitting to be a city
I'd agree with the "Greater Bournemouth" suggestion - surprising in a way that it isn't already (but then I'm far far away and don't keep up with the local rivalries - I certainly know of a few conurbations where the "junior partner" has been uneasy about being subsumed into the larger place - I've known people from Leith still bitter that the important port is now just seen as part of Edinburgh!)
"Brighton and Hove" doesn't sit great with me - it's certainly a large enough place and a regional centre but for me a city has always been one place, rather than a collection of towns (Stoke is always an oddity) - I could see the logic in "Greater Brighton" but incorporating both names feels cheating!