What you heard, IME, is the best feature of Frank's tonearms (aside from their gorgeous looks perhaps). All Schroeders are excellent at damping stray energies escaping from a cartridge. The higher up the model line you go the better they get in this respect (and others). This gives them the ability to tame cartridges that can sound shrill or clinical on other arms.
The most striking example I've heard was with a Shelter 901. That cartridge had great macro-dynamic punch but it also leaked tons of energy into a tonearm. Most arms can't handle that so the 901 often sounded edgy, over-excited or disjointed. In my own experience it behaved that way on a Basis Vector, Graham 2.2, Origin Live Silver and TriPlanar. Mounting it on a Schroeder Ref provided a mind-altering experience. The sound settled down to a calm, integrated wholeness that let the music sing. It was shocking to hear how much a well damped arm could tame a basically unbalanced cartridge.
If you use a better damped cartridge, that particular Shroeder advantage may be less significant than other parameters. For example, a TriPlanar is certainly less well damped but it provides more accurate setup and greater stability. That can make it a more effective platform for well behaved cartidges. It's all about component matching, as usual.
Of course we'd all prefer an arm that offers the best of everything! I've used one arm that betters a TriPlanar's setup accuracy and stability while also handily beating a Schroeder Ref for damping of stray energies. It's altogether more holistic, dynamic and accurate than either of these fine arms. Pricing is similar to a Ref, lead time is perhaps a bit shorter.
The JMW is a decent mid-market arm, but comparing it to top tier arms that cost 2-3X its price isn't quite fair.
BTW, a turntable rarely has much impact on how a tonearm performs. Aside from obvious errors like mounting a very heavy arm or a linear tracker on a lightly sprung table and screwing up the suspension, arm/table interactions are fairly insignificant. Almost any arm would perform close to its best on an HRX, or on my Teres, or on a host of other good, stable tables. OTOH, arm/cartridge interactions are vital, as you just heard. That's the interaction one must consider when selecting a tonearm.
