I don't know about other sources, but in the Twilight of the Clans novels, Lincoln was described as being a tactical genius but not particularly skilled at strategic-level operations, which was a liability for someone of his rank because it to him micromanaging things.
He is indeed mentioned as a tactical genius in Grave Covenant, and for some reason the people there equate Tactical Genius with Strategic Dunce. There are a couple of write ups where he is referred to as a Strategic Genius, but for the most part it isn't mentioned. Or contradicted, at least, explicitly.
Consistency has ever been a problem and the same lack of information that lets players infer their own interpretation of the Jaguars also works for authors. Which explains the somewhat contradictory stance on artillery and freebirth troops, amongst others.
Reading a bit between the lines, and trying to make sense of all the issues involved, my reading would be that Lincoln Osis was indeed a tactical and strategic genius. The IS feared an Osis led invasion and did so with cause. As ER62 says, he would have been a terrifying war leader
Where he failed...and what caused him to make mistakes...was his personality. He was a glory hound, an ego maniac and he lacked confidence in himself. He was as likely to make a decision based upon how he believed it would reflect back on him as he was to make one based on tactical or strategic values. An example is when he tried to emulate Howell on Tukayyid or tried to shift the blame for the failures of Luthien and Tukayyid, or ordered the Sixth to abandon its positions simply because be felt defensive tactics would make him look bad. He was a Khan able to sacrifice his own Clan to make himself look good.
There are also a couple of scenes which make me think he was losing support within the Clan....that would make sense given a string of high profile failures during his tenure and the blatant corruption he showed by retaining the Khanship after bring elected ilKhan, but it could also just be the way I read it. If so, he would be under a lot of pressure to maintain support inside the Clan as his supporters melted away.
So...whether he was a strategic genius or not would depend on how much of his ego and insecurity he could put aside.
Which...if he were winning...would be easy to do, and so make him doubly dangerous. Its one reason why an Osis led invasion was considered so dangerous for the IS.
But...when losing...putting his ego aside would be difficult, and he would increasingly make decisions based on his own need for glory and political security. Making him a huge liability for his own Clan during Bulldog and Serpent. Which he was.
But as I said, that's my reading and the info we have is vague enough others are possible. But I like this as it provides, to me, a better explanation for the Jaguars collapse than "they were so unprepared for the invasion they had spent years preparing for and would have launched months previously that they armed themselves with guns"