In a way no Lend Lease in a TL where Britain had greater industrial capacity would make the UK much worse off.Of course they DID.
Britain's debt after ww1 would have been far lower than IOTL if its industrial capacity was bigger. Britain with a bigger industrial capacity than IOTL would have been able to supply France and Belgium what these countries and even Britain itself IOTL relied on American imports, thus saving lots of their reserves (for both UK and France).
Next, for ww2, being less reliant on Lend Lease would have make UK much better off post war.
That is British industry might be able to satisfy all the British armed forces needs, but the Treasury would have to pay for it. Lend Lease was for free. Therefore the extra production would produce a larger National Debt after the war, meaning more interest to pay on said debt and less money to pay for things like the new Welfare State.
The ideal situation for the UK would have been able to build all the equipment that the USA supplied for free under Lend Lease, with the US Government still paying for it. But I don't see President Roosevelt being that generous even if Congress and the American people would allow it.
Where having more industrial capacity would help is the period before Lend Lease and after World War II, which in British history is known as the Austerity Era. Before Lend Lease it would have meant the British foreign currency reserves would not have been exhausted so quickly. However, even then the need to import so much wasn't because of the weakness of the whole of British industry, it was because the arms industry had been wound down too much after World War One.
The ability to produce more goods would have been good for the post-war Export Drive and at the same time allowed more for the home market so that Austerity would have been less austere. However, the benefits of that would have been offset or even cancelled out altogether by having an even bigger National Debt. Furthermore as I've been saying about steel, its not enough to be able to make more. You have to be able to sell it at a competitive price and still make a profit.