Should I ditch the 3-gang Big Blue?

I don't think you need Centaur for chlorine.

Regular GAC will be fine. GAC has a great ability to remove the majority of chlorine even with minimal contact time. Now... according to the manufacturer, you need a 4+ cu. ft. system...

This is for organics, solvents, etc removal, simple chlorine will be just fine with a 2 cu. ft. system.