That argument does not work as +Liénart alone ordained +Lefebvre. Majority of theologians held that one can not be consecrated a bishop without first having been ordained a priest.
I would look into the allegations of +Liénart being a freemason. From what I understand they are at best questionable, having appeared (without a source(?) shades of The Angelus??) in a later edition of the list of Freemasons in the Church hierarchy...although +Lefebvre *allegedly* stated that he believed +Liénart to have been a Freemason (*allegedly* in speeches on May 11, 1976 in Minneapolis, MN and May 27, 1976 in Montreal, Québec) and +Williamson did in EC No. 450 "Bishops Valid? -II" Feb. 27, 2016: "The Cardinal [Liénart] was a leading neo-modernist at Vatican II, and surely a Freemason himself."
I am really quite ignorant about this topic. Are you saying that only one bishop ordained Marcel Lefebvre?... which is probably the norm. But then, why do other priests normally impose their hands on the newly ordained priest? Isn't that to ensure that apostolic succession is guaranteed? I never really thought much about this topic of our founder.
Re: +Lienart...Aren't those two references May 11, May 27 1976 readily available to listen to? "allegedly" could be verified and determined as fact, and further discussion can move on...
AI Overview

Archbishop Marcel Lefebvre was consecrated a bishop on September 18, 1947, in Tourcoing, France, by Cardinal Achille Liénart, the Bishop of Lille. The co-consecrators for the ceremony were Bishops Jean-Baptiste Fauret and Alfred-Jean-Félix Ancel.
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The episcopy is the Fullness of the Priesthood, but I appreciate your doubts. All this must have been scrutinized decades ago, no?