I just want to chime in here and agree with this wholeheartedly.
There is a lot of self-fulfilment when it comes to London spending vs London generation of revenues.
It's famously the case that London props up almost the entire rest of the country. Scotland itself being a net-loss in terms of GDP.
I come from a City called Coventry, "investment" in the city is non-existent; the only investor right now is the University which has essentially bought the entire City over the last 10 years.
Why? Because "Coventry doesn't make money". Why does Coventry not make money? -- well, companies would never headquarter there because the infrastructure is not good enough and the networking connections are not compelling; even if you think it will save you money because it's cheaper to hire in Coventry (somewhere in the order of 1/3rd london salaries, 1/5th London commercial rents) it's still awkward because navigating the city requires making use of the awful public transport or buying a car[0] (which the city is close to capacity with already!)
Birmingham, Britains "second city" has only moderate investment compared to London (though insanely more than most other UK cities), but also feels destitute in the majority of areas, _especially_ when compared to London, the infrastructure is marginally better than Coventry but the prestige/networking/access is nearly no different.
This is many decades in the making, there is absolutely no way to compete with a city like London which is reaping the rewards of many decades of incredible investment which creates network effects which only serve to increase the gravitational pull of the city.
[0]: https://youtu.be/Mxvk3KO8p20