Hi fretnoise,
Yes that's possible to use (i have allways done that) in some situations - and even desired, if you don't wan't to use the ADSR Retrig Playmode to get none retrigger functionality. But it can only be desired because the Playmode unfortunately in Retrig position does'nt retrigger a held note when you try to do trills holding one note while rapidly playing another note multiple times, - and that i actually see as a bug.
Using 1 voice poly is'nt the same as using mono mode.
(In some cases you perhaps also wan't to switch between mono and poly mode without using the voice selector.)
(A strange thing is, that the original ARP afaik has high note priority, while the minimoog had low note priority like Arturias ARP has now.)
Personally i think ARP 2600 need to be rebuild, as there are other things that's missing or could be better like the sound and behavior of the filter, adding the originals internal audio feedback option and adding the originals dual direction functionality for the Electronic Switch.
ARP 2600 is quite old like some other Arturia synths that also could use a rebuild, as technology has improoved much since they were made.