We've been following the UKs lead for the last seven years, so I can't dispute that. Let's hope we both get back on track.
Firstly, the UK remains a world power (if diminished), a nuclear power, a major top level military nation, and London is the finance capital of the world. Economically, politically, technologically, militarily and culturally, the UK remains a major world force. From banks to the SAS, from pop music and TV/films to technology.
I am not sure about the 2008-2015 comment. In fact in that time, the UK has gone right politically, balanced the budget, strengthened the UK economy, UKIP is the biggest new party, support for an EU exit is fast growing.
Yes, the world needs a strong US with the UK backing it as its main powerful ally.