Am I correct in thinking that a non-Schengen to Schengen transfer is likely to be both simpler and quicker at Amsterdam rather than Frankfurt?
Your thinking is correct. Schipol airport has just one enormous terminal building, on one half of the terminal all gates to Schengen destinations, non-schengen the other half. There is a single corridor that links the two sides with an immigration checkpoint in the middle. Couldn't be easier.
Good. Thanks for confirming that, Michael S.