really nice car you are maintaining masha allah if i haven't said before.
although 2 and L are moostly intended for downhill, currently have 4 automatic cars out of 5 in house and have mostly owned automatics in the past, theres no harm really in driving in 2 or L up hill etc if you want too, it is mentioned in owners manual that if you want to tow something use 2 or L which shows its for stressful situation not just downhill situations.
i also find that in cars which have 2 or L less accelerator is required to be pressed to maintain speed going up a steep ramp then in D such as in my 2006 altis which has similar transmission as yours only with the addition of ECT power button. its probably down to the fact that theres more slack in the torque convertor in D then in L etc
for those who think transmission gets over heated, i have a OBD scanner and in altis it also shows transmission temperature, i found no abnormal increase in temp when accelerating full thorttle on a flat road in L and maybe changing to 2 but not with foot on accelerator.
so factually it shouldn't cause any overheating in long run too. and theres a reason we change ATF fluid after 60k and not lifetime as indicated on some transmission, thats to take care of any such driving situation or stress the transmission takes. if someone is still worried he can change the ATF a little early then.
i hope i have made any confusion about this topic clear:)