What do you mean sort of? The belt decouples all motor vibration from the turntable. The Thorens TD 125 has a superb servo controlled motor with unmatched speed accuracy. It is widely recognized as one of the finest turntables ever produced. Many, if not most were produced without PU arms, and the owner fitted an arm of his choice, which is the case with the OPs purchase and has been fitted with an SME series II arm.
He has purchased a renowned and widely admired classic turntable that will deliver superb performance.
A really good turntable should ideally have cartridge and PU cartridge designed as a unit. In the case of my TD 125 this condition was met.
For optimum results the arm and cartridge should be designed as a functioning unit and designed to work together. It is especially important to match arm resonance to the cartridge compliance.
In the turntable below, SME designed there series 3 arms in cooperation with Shure to match arm resonance and moving arm mass and also provide a silicone fluid damper.
That rig is at the pinnacle of LP reproduction.
My Thorens TD 150 also has the same arm cartridge combo.
Decca knew that arm and cartridge should be an integral design, and so designed it so that most of their cartridges had to be fitted to a Decca arm.
In the turntable above, Peter Walker designed the Quad 22 phono stage to optimize those Decca variable reluctance cartridges.
The OP has played many of his LPs here and has been astounded at how good LP reproduction is. That is because care has been taken to optimize the integration of all the components.