Remember though that this annoying fact isn't only true of zones 7-9. That is equally true of zones 2-6. The general TFL not having non zone 1 caps is a universal annoyance.
Absolutely.
Sorry, maybe it doesn't come across properly. The point I am trying, possibly badly, to make is that the only daily cap available assumes you travel into Central London and it seems quite unreasonable that you can spend all day travelling in Zone 1-2 for £7 whereas if you took a number of journeys wholly within Zones 7-9 the cap only kicks in at the level that assumes you have gone into Central London.
Well here you have people from Z2 doing what you think is unfair for Z7-9 people to have to do: travelling into Central London.
Let's look at Z2 on it's own: £1.70 peak fare, £1.50 off-peak fare, £7 cap. That's 5 journeys to trigger whatever time of day. Pointless unless going to zone 1.
Off peak, any journey within zones 2-6 would be £1.50 (and the most expensive peak journey: Z2-6 is only £2.80). Caps are £8.20 for Z3, £10.10 for Z4, £12 for Z5 and £12.80 for Z6. It's all just useless unless going to zone 1 - and then they would still mostly need two Z1-2 journeys to reach it unless two peak fares from/to the outer zone to/from Zone 1.
Let's look at commute in, work, go somewhere else in Z1 for leisure in the evening, go home. A common thing. The worst is Z9, Z8 next, then Z6, Z7 and Z5 all on the next tier (another journey in Z1 is all that's needed), with Z1, Z1-2 and Z1-3 needing just three journeys to cap.
Z1 - a peak journey in = £2.40, a Z1 journey = £2.40, an off-peak journey out = £2.40. Total = £7.20 , cap = £7.00, needed to cap =
-£0.20
Z2 - a peak journey in = £2.90, a Z1 journey = £2.40, an off-peak journey out = £2.40. Total = £7.70, cap = £7.00, needed to cap =
-£0.70
Z3 - a peak journey in = £3.30, a Z1 journey = £2.40, an off-peak journey out = £2.80. Total = £8.50, cap = £8.20, needed to cap =
-£0.30
Z4 - a peak journey in = £3.90, a Z1 journey = £2.40, an off-peak journey out = £2.80. Total = £9.10, cap = £10.10, needed to cap = £1.00
Z5 - a peak journey in = £4.70, a Z1 journey = £2.40, an off-peak journey out = £3.10. Total = £10.20, cap = £12.00, needed to cap = £1.80
Z6 - a peak journey in = £5.10, a Z1 journey = £2.40, an off-peak journey out = £3.10. Total = £10.60, cap = £12.80, needed to cap = £2.20
Z7 - a peak journey in = £5.60 , a Z1 journey = £2.40, an off-peak journey out = £4.00. Total = £12.00, cap = £14.00, needed to cap = £2.00
Z8 - a peak journey in = £6.90 , a Z1 journey = £2.40, an off-peak journey out = £4.00. Total = £13.30, cap = £16.50, needed to cap = £3.50
Z9 - a peak journey in = £7.00 , a Z1 journey = £2.40, an off-peak journey out = £4.10. Total = £13.50, cap = £18.30, needed to cap = £4.80
and the same for off-peak. Zone 9 gets within a Z1 single fare of the cap, but Z7 and Z8 don't quite get there. Things get worse for outer London: Zone 3 needs another journey now to cap, Zone 4's fourth journey needs to include Z1 now, Z5 is a long way off and Z6 even worse (2 return trips to Z1 wouldn't be enough)!
Z1 - an off-peak journey in = £2.40, a Z1 journey = £2.40, an off-peak journey out = £2.40. Total = £7.20 , cap = £7.00, needed to cap =
-£0.20
Z2 - an off-peak journey in = £2.40, a Z1 journey = £2.40, an off-peak journey out = £2.40. Total = £7.70, cap = £7.00, needed to cap =
-£0.20
Z3 - an off-peak journey in = £2.80, a Z1 journey = £2.40, an off-peak journey out = £2.80. Total = £8.00, cap = £8.20, needed to cap = £0.20
Z4 - an off-peak journey in = £2.80, a Z1 journey = £2.40, an off-peak journey out = £2.80. Total = £8.00, cap = £10.10, needed to cap = £2.10
Z5 - an off-peak journey in = £3.10, a Z1 journey = £2.40, an off-peak journey out = £3.10. Total = £8.60, cap = £12.00, needed to cap = £3.40
Z6 - an off-peak journey in = £3.10, a Z1 journey = £2.40, an off-peak journey out = £3.10. Total = £8.60, cap = £12.80, needed to cap = £4.20
Z7 - an off-peak journey in = £4.00 , a Z1 journey = £2.40, an off-peak journey out = £4.00. Total = £10.40, cap = £12.90, needed to cap = £2.50
Z8 - an off-peak journey in = £4.00 , a Z1 journey = £2.40, an off-peak journey out = £4.00. Total = £10.40, cap = £12.90, needed to cap = £2.50
Z9 - an off-peak journey in = £4.10 , a Z1 journey = £2.40, an off-peak journey out = £4.10. Total = £10.60, cap = £12.90, needed to cap = £2.30
All this is just working with the TfL-LU fare scale. Using the TfL-Ang, NR-1, NR-1T, NR-2 or NR2-T fare scales would make it more likely to cap as singles are more expensive.