Most vaccines contain the actual virus. This vaccine does not.

Some of them are traditional inactivated virus vaccines. If that's your only point of concern, you should simply be advocating for J&J.

All of them still work by teaching your own immune system.

the difference with the J&J isn't the payload (spike protein), it's the delivery mechanism (adenovirus vs. mRNA)

That's not quite correct. Neither contains the spike protein. The delivery mechanisms are two different ways to tell the cells to produce the spike proteins. The immune system then learns how to respond to the spike protein presence.

The mechanisms are the payloads. They're different formats of the spike protein recipe.