There is plenty of thread engagement. If the heli coil is too long I cut them with a pair of dykes. You are way over thinking this. However if a vehicle had been returned to me in that condition I would be back in the service drive having a conversation with the service manager. They should fix it at no charge.
One problem with the sealer is many guys don't know how to use it properly. The surface must be clean, oil free and dry. A 1/8" bead is all that's needed, excess will fill the blind hole and pop the threads. Do not wait to assemble the components after laying the bead. Don't wait for it to skin over or set up, assemble within 10 minutes then allow it to set for 30 minutes. The biggest thing is that the surfaces are absolutely clean and dry. That is hard to do on most transmission/transaxle pans that are still in the vehicle but it is possible.