You can upload photos into the new iPhone app in batches of 20 and then sort them into observations from there. 70 photos would only be 4 batches and probably take about 10 minutes. This is also my default workflow and I’ll agree it’s tedious but less so than taking a DSLR everywhere and then transferring photos off it at some point later.
Alternatively, HEIC photos should be supported and it looks like this bug should be fixed relatively shortly.