Good points. I agree with almost everything you say. Only the 1-2-4 system on electric bass is mostly applicable and usefull in the lowest 5 or 6 frets. From fourth or third position 1234 is no problem even on fretless. Even in the lowest region you can still use 1234 on fretless. Many pro players do so. But I agree that 1-2-4 can be handy in those lowest positions and give your hand some rest. You don't need to master upright bass fingerings and positions though to master fretless bass. Although it will not harm you.
(higher up on the fingerboard, 1-2-3-4 becomes quite manageable). (To be complete, one should point out that some players play 1-2-3-4 everywhere on the neck on fretless, and some do this even on the DB; but this requires to use a pivot technique that is somehow more advanced and anyhow requires a specific training as well).
Concerning the use of 1-2-3-4 technique on higher regions of the fingerboard, we are saying the same thing. Where to transition from 1-2-4 will is player-dependent: for me (small hands) it is between 5th and 7th "frets".