The Quebec Agreement, on the whole, was wildly in favor of the UK. By the time the UK was negotiating it, the US had far surpassed the UK in terms of nuclear development, and had, in the eyes of the top US technical advisors (e.g. Vannevar Bush) and military advisors (e.g. General Groves) absolutely no need for collaboration with the UK whatsoever. It was only Churchill's appeal to Roosevelt's sense of the "special relationship" that got them the Quebec Agreement at all, and essentially let the UK piggyback on US developments in reactors, enrichment, and even bomb design.

So point 4, which I presume you are indicating:

Fourthly, that in view of the heavy burden of production falling, upon the United States as the result of a wise division of war effort the British Government recognize that any post-war advantages of an industrial or commercial character shall be dealt with as between the United States and Great Britain on terms to be specified by the President of the United States to the Prime Minister of Great Britain. The Prime Minister expressly disclaims any interest in these industrial and commercial aspects beyond what may be considered by the President of the United States to be fair and just and in harmony with the economic welfare of the world.

...was meant both as an acknowledgment that this was the US doing the UK a huge favor, but also meant to defang accusations (from the aforementioned scientific and military advisors) that the UK was only in it for the money. The stereotype that Bush and others believed was that the UK only cared about the postwar, and could not help with the wartime in any significant way, and that specifically they wanted to monetize peaceful nuclear power as soon as possible. The fact that UK efforts were coordinated by Imperial Chemical Industries was seen as reinforcing this idea (of course, major industrial contractors played huge roles in the US program as well, and were seen as all well and good, though they didn't run the show as much).

So this was a way for the UK to indicate that in the postwar they would defer to the US opinion on these matters, as a way of indicating that these stereotypes were false.

Was the Quebec Agreement a blow to British sovereignty? Probably not as much as it was a blow to US sovereignty (the US was not allowed to use nuclear weapons, or distribute information about them, without getting UK consent!), but to a degree, sure, yes, even though the Quebec Agreement stopped being in effect shortly after the war ended.

In practice, the Quebec Agreement was on dubious legal grounds anyway. It has the appearance of a secret treaty, not ratified by any legislative body. This led to many American legislators who heard about it in the postwar thinking it was totally ridiculous and non-binding for anybody. In the end, it was not very lasting. The UK still managed to keep a "seat at the table" even after the McMahon Act prohibited formal US-UK collaboration, because of a far more important agreement: the Combined Development Trust, which guaranteed the UK a large share of the world's uranium market, which the US desperately desired. And in the 1950s US-UK collaboration was able to resume again, but that's a different story.

On the Quebec Agreement, Hewlett and Anderson Jr.'s The New World contains several chapters about it, if I recall correctly, and makes quite clear how angry many of Roosevelt's advisors were about it being proposed in the first place, because it was so blatantly favorable to the UK.