Those seat tubes do get ovalized ! I had to recently work on a Trek a customer brought in, results of a poor shipping job.

Could not get the post out so went the cut off and saw it out route. Took 20 minutes or so. It was not too far in.

a check of the inside diameter was like what you found out, true in one direction but lacking in another. I had to send it to another shop in town to have the tube honed true.

Happy customer. Good luck with your project within a project !