No, this is not true at all. Look at Edward James Olmos' Adama (if you're familiar with BSG). That character had way more conflicting motivations than Archer. It enhanced his performance. Most actors feel that the more conflicting things going on with the character, the better the role. Olmos is another actor who I've imagined as Archer. I used to compare the two quite a bit when BSG and Ent were in production. Actors want demanding roles where their character is pulled in several different directions at the same time. That is what creates great drama.
If you're talking about the often brought up week to week character changes to Archer, I say again, a better actor might not have liked the changes but would have still been able to credibly drag his character through those changes without sacrificing Archer's dignity (well, too much of his dignity) and audience respect.
Actors sometimes go on auditions and may several completly different characters in the same day or several different versions of the same character in one audition. Why would a professional actor not be able to handle week to week changes in his character's personality?
You need not sell me on Olmos' abilities. Mijo did more acting in a coma that the rest of the BSG cast. Bakula and Trinneer can't hold a candle to Olmos.
However, his abilities are not germane to the question of Trinneer's ability to play the role of Archer as written