The phrase "as first assumed" is correct and usable in written English.
It can be used when referring to an initial belief or hypothesis that was made prior to further investigation or evidence.
Example: "The results of the experiment confirmed the hypothesis, as first assumed by the researchers."
Alternatives: "as initially believed" or "as originally thought".
"We don't really want the bullshit and optimistic stuff that Michael has written... .. Phil Jones, UAE, to Jonathan Overpeck, Arizona University, 8 February 2008 email 30622) Jones is referring to new research by Michael Schultz of the University of Bremen – not, as many at first assumed, Michael Mann.
Nor is Soderberg's repeated intrusion of headline events into this love story as frivolous as one may at first assume: on the contrary, it reminds us that there is a world out there, that there are other lives and loves and duties, that time goes on, that everything ends.
Resolving the signalling role of His kinase activity has not been as simple to accomplish as one might at first assume.
It did not include an officer with experience in maintaining a large force over a native carrier line, and therefore took time to realise that the Japanese force could not be maintained over an inland track, as was first assumed.
It soon emerged that the strange bear was the making of Russian artist Viktor Ivanov, who created the meaty ted out of chicken rather than turkey as was first assumed.
Both Nigella and Annie Bell's recipes are for "boiled fruit cakes" – which doesn't, sadly, mean that the cake has literally been boiled in pursuit of that ultimate moistness, as I first assumed, but that some of the ingredients are boiled during the preparation of the cake.
Mr Allawi, who had hoped to be president or prime minister, is yet formally to accept his appointment as head of a "higher policy-making council" which, though its powers have not been spelt out, may have a wider brief than security, as was first assumed.
Recent reports have indicated that the attack on the compound in Benghazi may have been planned by a radical Islamic terrorist group, rather than being the result of protests that got out of hand, as many first assumed.
None are exactly as simple or as uniform as you first assume.
Hearing high-pitched cries, they looked out to sea to find that the source of the noise wasn't birds (as they'd first assumed) but Eritrean migrants shouting for help, their bodies thrashing.
