y not wrote: “Is it not that once on the Path, one needs no external help until one reaches Arahanthood?”
Yes. But causes are not enough in Buddha Dhamma; suitable conditions must be there too.
– However, suitable conditions will appear in due time. That is called the “nature of things” or “dhammatā”.
– For example, a Sotapanna (or a Sakadagami anugami) may not make any progress in a particular human birth (due to unfavorable conditions), but will catch in future births in due time.
“so progress will be made even outside of a Buddha sasana.”
No progress can be made outside the Buddha Sasana.
– It must be noted that the time limit for Buddha Sasana of 5000 years or so holds only in this “human world”. That limit is not there in deva and brahma worlds.
– Buddha Sasana in the human world ends when the last Sotapanna (and of course any other with magga phala) have all passed away. But they may be reborn in higher realms and can take a much longer time to get to the Arahanthood.
– For example, a Sotapanna deva may attain the next stage much later than 5000 years.
– There are brahmas in higher brahma realms who had attained the Anagami stage during the time of a previous Buddha who lives several maha kappas earlier.