You are presenting a false choice. The choice is not "centralized systems" OR "everything in Bitcoin". There are many options to build non-centralized ways of settling payment on a decentralized Bitcoin— ilpirata79 linked to one such approach. A lack of care into the operating costs of Bitcoin nodes may result in Bitcoin itself becoming effectively centralized, which is an outcome which would make building a non-centeralized payment method on top of Bitcoin pointless or impossible.