So, the AA option is madness, right...?
Not necessarily, it depends on how much you need the extra tier points. If you do go for the LAS-JFK-LHR option then note that if booked via ba.com as a WT+ ticket then it's likely that the LAS-JFK will book into flexible economy and hence earn 70 TPs not 35 TPs so the return trip would net you 320 TPs total via JFK compared with the 180 TPs for the direct flight. As you say the disadvantage is spending several hours in AA Y (*).
(*) If there's availability you could always upgrade the AA Y to the next class.