What does "if vexed" mean in this context below?

He approached English linguistic and literary conventions aslant, but the seeming handicap of his foreignness helped him bring to the English novel a fresh geopolitical understanding, a formal seriousness, and a psychological depth, all of which opened up new possibilities for imaginative literature in English, as indicated by his profound, if vexed, influence on later writers as different from himself as the Nigerian Chinua Achebe and the Anglo-Trinidadian V.S. Naipaul.