[Iscool]

All that you say about prostration makes complete sense to me and is also common in my tradition, with the same inner meaning.

It is common in many Protestant denominations but they don't bow to the pastor as this priest is bowing to a bishop...

It is very common for these same people to bow to statues of other Catholics...

[Salvation]

I think you are misinterpreting the picture.

The prostration indicates the ordinand’s total commitment to Christ and to his ministry as a priest serving Christ.

[A.A. Cunningham]