As an owner of a Ref 2se and a Ref 5se, I would be very interested in what your review found if you were open to sharing it.
Regarding the ARC Ref 3 phono compared to the 2se and RP10 phonos... Looking back on my notes (circa 2017) I can say a litle bit, but here won't give supporting music examples which I have in spades and which a thorough review includes.
All units (2se, 3, RP10) share the characteristic modern ARC house of sound of general clarity, air, spaciousness and a well represented soundstage. No mistaking any of these for other than an Audio Research product. Among themselves there are of course differences. My very first reaction to the 3 (direct from my notes) was: "its different - I'll need time to assess it; I had no immediate sense on how it was different, but it is different."
My next note reads: "Elves and Dwarves - the 2se has a slight upper mid-range emphasis while the 3 has a slight mid-bass emphasis."
Compared with the 2se, the 3 has a fuller, weightier sound that is more forward whereas the 2se is a bit lighter and not quite as articulate in the mid and lower bass. The 3 is a more mature sound than the 2se, it is more muscular, more controlled with slightly better texture and discrimination among instruments in space. Dare I say more masculine. I was of mixed mind wrt the 3's forwardness - it was punchy with drive and motivity but that characteristic struck me as somewhat hi-fi, lacking the balance of the 2se - it was bit forced and less natural. While their differences were not night and day, overall I found the 3 an advance over the 2se, overall it is a more complete phonostage. Having owned a 2se and 5se, they remain an excellent combination
Comparing the 3 to the RP10 was a different story. Architecturally the RP10 is two 2ses, one for each channel and each with its own power supply. The RP10 is superior in every aspect; it is more refined, transparent and balanced as reflected in the difference in price. I could go into detail on differences here, but hopefully that will suffice. On the used market the RP10 is a great value given the price of a new 3se.
As you know, the Ref 3 was upgraded to the Ref3se which I have not heard but from what I've read (hearsay) the sonic differences are not as great between the 3 and 3se as they are claimed between the Ref 6 and 6se linestage. Ymmv, the best assessment is to listen to a unit in your own system. Let me know if you have specific questions.