I don't think it is accurate to characterise st paul's as being lost in a sea of skyscrapers as the cathedral is protected by a plethora of sight-lines. It is basically impossible to build tall if an area is covered by a sight-line, and some of them are quite absurd - for instance the viewing corridor from Richmond park, the old royal hunting grounds, which blocks development for a 10 mile stretch because Prince Charles or whoever is nostalgic about the view from one small patch of grassland.
Also the UK has a rather different approach to wealth than the US - it's banking sector always favoured discretion (even today hedge funds prefer to set up in discreet offices of domestic scale hidden away in Mayfair), and historically wealth has been hoarded by the aristocracy and upper classes, who were nervous about extravagant displays of wealth pissing off the lower classes. Less Manhattan, more Zurich. Only in recent decades has this changed, and though the class tension still exists, it may be that more talls is a sign the UK is no longer quite so hung up on class divisions.
That said, 20FCS (the walkie-talkie) is a mistake. You'll struggle to find a more offensively corporate building anywhere - not only is it aggressively top-heavy with its bulk at the top, but it reflects the sun downward, melting the poor peasants on the street below. fugly.