I don't get this at all. He's got us in 8th place, genuinely challenging for a place in Europe. Is he fantastic? No. Is he bad? No. He's pretty much the same manager as Nuno, getting the same kind of play and the same kind of results. The difference is Nuno did it with the squad he built, playing the way he built it to play and Bruno is doing it with a squad he inherited and playing in the only way Nuno's squad can play.
Surely the time to judge Lage is when he has had the opportunity to build the squad in his image, playing the way he wants to play? If the style and results deteriorate then you have grounds to say he isn't very good. Saying it now just makes it seem like you're saying it because that's what you said when he was appointed and because you didn't want Nuno sacked.
My opinion on Lage is that he has strengths and weaknesses, he's done a lot of good but also made a lot of mistakes. The players clearly like him and respond well to him, and he seems to be a very good coach. His downfall seems to be picking random weak teams for no explicable reason, and being quite slow/poor to make in game changes. Part of that could be that the players he has available aren't adaptable enough to play the way he wants and seem to revert to Nuno's way of playing as a safety net.
I'd give him another season with a changed squad to see if he can progress before writing him off as 'not very good'.