I'm afraid that it's you who has failed to move on. The notion that fungi weren't digesting lignin in the Carboniferous has long been debunked. There are other reasons a-plenty why coal deposit formation peaked (but did not disappear) at that time. Like all living organisms, fungi require the right environmental conditions in which to operate effectively. Those conditions were denied to them in many areas during the Carboniferous, particularly in anaerobic, acidic swamp conditions, just as today in modern peat deposits. Your pursuit of that line of enquiry, should you go in that direction, would bear fruit.