Your hearing is fine. The Verdier has a very relaxed quality to it which can easily be lost with mods. The supplied rubber belt is very poorly made, it is out of round ( cross section ), rough, and in my experience you can see it riding up and down the platter as the platter rotates. A fellow user local also has this problem. The Leonardo rubber belt is better made ( more true ), it's as simple as that.
I used the supplied linen thread which I preferred to the rubber. I would not use cotton ( stretches ) or dental floss ( too waxy ) both of which I have tried on my reference TT and were failures.
On my reference turntable ( 26kg platter ) I use surgical silk. If you use low tension you can chalk it but I don't.
I don't see why you should lose anything with a better motor as long as you run the belt with low tension. However my guess is that the Sota Eclipse motor is closer to the original in drive, just more accurate.
As an aside I sold the Verdier tp a friend who had a SME20 - the Verdier was significantly better than that TT.