> The ETA app gives you fast feedback on whether or not photos that you need to provide are any good, handles state, retries, talks to the NFC in your passport, handles long running workflows and validation etc.
Apart from NFC all of that can be handled by a 1990s PHP application.
> The web is not a panacea but there is still the backup option which was clearly found.
Where by "clearly" you mean "multiple clicks to get there while being aggressively upselled the app like it was a commercial website".