Not knowing the full scenario, I'm not sure what advice to offer. It sounds like it ran about how it should.
By my calculations, that was a "moderate" encounter. Something meant to use up some resources (like Turn Undead and
heat metal, etc.) but otherwise no real danger to the PCs. The fact that the wizard dropped as well was pretty much the goal. Did the gargoyle double-tap the wizard to finish them off? Or the gargolye could have threated to kill the wizard unless the PCs surrendered? Or the gargoyle could have grabbed the unconscious wizard and flown away with them.
Unlucky rolls by the PCs and luck on the foes side might result in more of challenge, but probably not notably so.
Some points, however, in case these were things you might have overlooked?

(to be clear, I'm not saying you
did, only you might have)
- Drow faerie fire would make the Gloomstalker visible.
- Being invisible is not the same thing as being hidden.
- You (generally) cannot take the Hide action if you are directly observed.
- Although the Cleric is tanking, unless it is a bottleneck, creatures can choose to attack whoever. The drow could have shot whoever.
- The gargoyle (with flying speed) should engage the ranged targets.
- When creatures can't "hit" a PC, grappling them is usually a better option. Then take the PC to the ground so others have advantage to hit in most cases.