On your second sentence, I’ve noticed “overtaking buses” where a night bus and day bus have a section in common. There could also be a legit reason if the second bus is about to terminate while the first bus picks up loads of passengers!
However, as far as advice to customers goes, I think we’re looking at a mote rather than a beam. The beam being that if there are high frequency and low frequency alternative buses, the service interval is “helpfully” added to the overall time for the former and not the latter. Enfield Town to Chase Farm Hospital is a good example with two low frequency routes (313 and W9) and one high frequency (every 8 minutes) route.
The actual journey time is not that different on each but adding 8 minutes to the W8 time messes things up, the consequence being that Journey Planner advises the low frequency service more often that it should.
The added problem with that journey is that each route serves a different stop in Enfield Town, so someone directed to the 313 or W9 would not be able to take advantage of the W8 which would often arrive sooner.
I think this is by design and I kind of get the logic - that high frequency services aren’t meant to run strictly to a timetable - but the consequences can be bizarre. Also I note that the service interval is not added into overall times for journeys on high frequency tube services, so it is not internally consistent.
Michael (complete with bee in bonnet)