A perfectly acceptable method of what? As you said, an alignment aid, sure. For creating a strong joint, no. For building anything structural, no. Building something that will have to securely hold hundreds or thousands of pounds, no way in my shop. I can tear a kreg drilled frame apart easily. I've done it. Can't break apart a m&t without destroying the work piece.
The domino is also a crutch tool that creates a time tested joint. Mortise and tenon construction goes way back. A floating long grain tenon adds strength to the overall joint.
Kreg jig has its place. Picture frames, cabinetry. I have it and use it.
Building an aquarium frame, I'll stick to what I know works. We all have our opinion of workflow. No one right way.