Ironically enough, new SMN is more limited as far as movement is concerned because old SMN could have 100% uptime thanks to Ruin II. While new SMN has more instacasts, a bad timing on Ifrit phase can and will hurt your uptime because you simply don't have a safety net enough. This is already enough to distance SMN from phys ranged, who simply won't miss a GCD or interrupt anything.

It's also disingenous to think that SMN has so much mobility while the other casters don't. BLM and RDM were already very mobile in ShB and they got even more mobile in EW. Not to mention how tanks and melee have mobility tools and ranged attacks that don't break combos anymore.

It's mostly about how easily accessible said mobility is. A good example would be Reaper's free dash and backstep VS Samurai's that cost kenki.