the view proposed by the book in the OP seems to be very much the product of a western, modern mindset -- suggesting, then, that there was no "real Christianity" until now. Our modern, especially NAmerican, culture is suspicious of any sort of demands placed on us outside of the work environment. We decry 'kingship' , and resent order, seeing it as abrogating "personal freedom".
leitourgia means the work of the people, laos - the people of God.
Work, work done in common, implies a template for common expression. Even Quaker meetings demand some basic 'rules' or common agreement - even if this is a meeting time.
when Christ was preaching 'on the grass', He was speaking to the as yet unredeemed. When He spoke to the apostles, and met with them after the resurrection, the tenor of the interaction was dissimilar to the mode with the crowds.
what seems to be 'relaxed' in the interaction with the crowds was in fact highly particularized to their spiritual condition; He was, after all, their creator, and knew them best.
also, the view which questions 'leitourgia' (a view which is, in my view, individualistic, and often self-serving - as opposed to community oriented), fails to consider the idea perhaps of self-denial, the re-shaping afforded by praxis. Children are taught first to not cross the street before they can fully understand the implications of the lesson. The benefit of praxis can only be fully understood by experiencing the results of doing.