From pearl harbor to Japan surrendered, US built 101 aircraft carriers, 300000 combat aircrafts of all types and have millions of men under arms. In what ways US need to kowtow to the British? Btw, in only in Tony Blair era did UK finally repaid the money UK own to US during the war.
It is a historical fact that back before WW2, America was NOT on the list of countries who led the world in technology. Britain was #1.
From various sources I have forgotten, there's a true historical account of what actually brought the US in WW2. Part of the agreement was a surrender of Britain's technologies to the US. You mention the other part. The final settlement of the lend lease act. A guy flew over with a briefcase full of Britain's top technological secrets and surrendered it to the US. That was part of the deal for the US to get involved.
Matter of fact is that the US leveraged WW2 so successfully to advance their technological and financial progress, that they developed a taste for it till this day. Anytime they need to prop up their economy a war starts.
What the US brought to the table that really turned the war in the Allies favour was manufacturing output and to some extent labour supply. They could outproduce anybody. They could not out tech anybody at the start.