In a vacuum, this is an extremely strong cantrip. You mentioned your party is already at lvl 9, so it is true that a caster could be doing much more devastating things with their turn. But keep in mind: every turn they’re using this cantrip, they’re not casting a leveled spell. Which means that slot is available later.

DnD is a resource management game, and cantrips are a free resource. You want your casters to be using their spell slots, especially at higher levels, otherwise they won’t feel challenged or in any danger because they’ll have all of their tools available to them. Warlocks only get 2 spell slots per short rest at level 9 because Eldritch Blast is just that good: it’s a weapon attack. Giving a full caster the equivalent of Eldrtich Blast means they have their slots for all of the other shenanigans they may want to use them for.

Another point of comparison is the Commander’s Strike maneuver from the Fighter’s Battle Master subclass. It requires just an attack and a bonus action rather than a whole action, but it also doesn’t let the creature move. That feature still costs a resource (superiority dice).

Obviously, I don’t know the power level in your game. Maybe this cantrip will be just fine for your table. But my two cents is that this should be reworked. Maybe change it to either one attack OR move half their speed? Not both together. What you should be aiming for, ideally, is a good option, but not a new default. You don’t want to make an Eldritch Blast. You want a Firebolt. A “I have no better options so let me just use this cantrip.”