even assuming that ...; even if we suppose that ...
Used to introduce a hypothetical premise, often in logical or argumentative contexts. The clause before と仮定しても is the assumption, and the main clause states what follows even under that assumption.
Even assuming he is the culprit, the motive is unclear.
Even if we suppose the budget is sufficient, this plan is difficult.
Combination of the quotative particle と, the verb 仮定する (to assume), and the conditional ても (even if). The phrase literally means 'even if one assumes that...'.