MCR and riichi are the two major competitive mahjong rule sets and are scored on entirely different principles: MCR counts fan against an eight-point threshold (3.8, 3.9.1), while riichi counts han and minipoints and has no equivalent minimum; MCR uses flower tiles and flower replacement (3.4.20)...
Why people argue about this
People often think that MCR's fan scoring is just about reaching an 8-point threshold, but they overlook the fact that it applies a sliding scale where fans below 3 points are worth less than 1 point each, unlike riichi which doesn't have a similar minimum for han and minipoints.