I wonder if end users can actually validate the rules of the drivechain themselves with affordable costs.

They were more worried about the idea that not enough end users would be able to run Bitcoin clients which fully validated all the protocol rules, which could undermine the decentralisation of the enforcement of the protocol rules.

- The Blocksize War Ch. 7 Bitcoin classic

https://blog.bitmex.com/the-blocksize-war-chapter-7-bitcoin-classic/