If you want an FAA licence (erm.....certificate) other than a PPL hanging on the back of a valid foreign licence then you *will* have to do a flight test as well as the relevent theory exam for the certificate(s). No get outs
AFAIK.
If you meet the ATP experience requirements then the easiest route is to do an ATP, and not a commercial + instrument rating.
Only a single exam + flight test to do. The slight downside is the tighter tolerance required for the ATP ie 1/4 scale deflection instead of 3/4. Might be a bit tighter on altitudes at the MDA too. Can't remember.
I converted to a US ATP-MEL in the mid 90s. It wasn't that hard. Trickiest part was remembering the US requirements w.r.t. approach lighting & vis. adjustments + the few regulatory requirements.
Last year I added ATP-SEL & SES in a single flight test using an amphib. Generally easy was my impression
provided you can fly to ATP tolerances.