If you want to use that argument, they both received the iPhone chip. Doesn't change that there are legitimate reasons to differentiate the balance between CPU, GPU, Neutral Engine and power consumption in an iPad vs an iMac. Give them two different variations of the iPhone chip then - my points still apply.
Nevertheless, until M1 was introduced, they developed chip variants specifically for iPad Pro, while the standard iPad always just used an iPhone CPU. It is not at all unimaginable to create a version specific for iPad Air and/or Pro.
That said, I would not be particularly surprised to see an M3. More likely than M4, in my opinion, but there is usually a reason for the leaked code names. I could be wrong, I just don't see them releasing M4 yet.