I really don’t see anything deserving of city status apart from a large population if that is a criteria. To be blunt, it’s a dump. Can’t see that it has any redeeming features TBH...
It has little (nothing, maybe a priory?) of real architectural or historical merit.
It has a very run down high street and shopping centre.
It has a football team in the at the bottom of the fifth tier of English leagues.
It has a muddy beach.
It has a ridiculously named ‘London’ airport (though not alone there of course) with a declining handful of carriers serving a dozen or so minor destinations.
We are told that becoming a city will give it a boost, well I'd have thought that towns should deserve and earn the status, not be given as a leg up to needy towns.
A place is bigger than one person, even a murdered MP and shouldn't be given city status on the back of this incident (possibly at the expense of other towns).