I don't remember that line in the VN, so there's a good chance it was either classic wiki fanon or a misunderstanding of a quote. Cu's always stated to be top-tier, from Saber saying he's the king of survival to EMIYA saying he's in the top three of all Lancers to everything he does and all of his descriptions in everything. But yeah, I don't think anyone will try and say Cu's anything less than first-rate.