Having just been through very very similar and having also followed the 'usual' advice of EW needing a later nap to encourage later waking, and having also had no luck this time (has worked a treat in the past)...my suggestion is to bring nap and BT earlier and see if you can lengthen both sleeps and recover from OT.
I agree that 9.5 to 10hrs over night is not enough, low sleep needs tend to get at least 10 or 10.5hrs over night.
I've had success with shifting nap an hour earlier and BT and hour earlier in the last week or so. Morning WU continued to be at (the suspected train time) around 5am, he was fighting the earlier nap and BT as you would expect because he is used to set nap and bed times so shifting took several days but he is already more willing for the earlier times AND has started to sleep past the train time! I suspect he was initially disturbed by the train, couldn't resettle but the result with set nap and bed time was an OT build up, making it even harder to resettle after 5am. Now that we've shifted the day and sleeping off the OT build up he is more relaxed and able to sleep past the disturbance.
We had
WU 6am shifting to 5am
nap 2pm - 4 or 4.30pm
BT 8pm
(and had this routine for months, it was fine for a long time)
now
WU 5 shifting back towards 6
nap 1pm
BT 7pm
The first day it took 45 min to settle him for nap, day 2 30 min, day 3 15 min. BT equally challenging first day but getting better.
He's taking a little time to get to sleep at BT, so S is coming around 7.20 meaning that even with the improved WU time we are getting about 10.5hrs night sleep (which is about normal for my LO).
Crazy as this sounds my LO did this last year approaching day light saving clock change too (and we shifted a total 2 hrs instead of 1hr, same when clocks change for winter another 2 hr shift!). I wonder if their bodies are picking up on a change in seasons??
If your LOs mood is deteriorating during the day (tantrums, grouchiness, looking like a zombie) I would certainly go for an hour shift on the whole routine to try to catch up on sleep (and don't cap naps). As awful as those early mornings are (I hate getting up at 5am!!) I find it preferable to have a 5am start and a happy well slept child rather than a grouchy one who tantrums all day. My own plan is to see where we are after the clock change next week and reassess sleep needs and nap/BT then.