3 CBs isn't necessarily a waste. Especially considering our CB options are quite good and you want to start Patterson and Aznou. Patterson has always been a bit shaky defensively, and Aznou is completely untested in this league. Playing them as wingbacks allows them to get the most out of their attacking abilities without them being too exposed defensively. Another bonus is that it's a system that pretty much keeps McNeil out of the side.
With our best XI available, I wouldn't be playing 3 CBs, but against a team like Brighton, with how they play, it could help us frustrate them.