Thanks for your explanation. It seems that 4 journeys in zone 3 + weekend extensions are enough to tip the balance to a bigger Travelcard if there is no discount.
However, will the balance be tipped to the other side if, instead, I have a suitable railcard for discounted off-peak travel, while still travel enough to max out on the PAYG all-day basis? My zone 3 journeys will most likely be off-peak, 2 on National Rail and 2 on TfL scale per week, but it can be more or less. I think that I tried to work out this situation in the past and got a conclusion that no Travelcard was a good value, because paying for 3 capped 1-2 plus 2 capped 1-3 worked out less than the 1-2 Travelcard plus the zone 3 extensions, but is it really possible?