I think you are correct. However over time I see the 2 chains diverging in that:
- Only some of the patches will be merged from ETH to ETC. (Ones that agree with the manifesto)
- Any patches that are merged across may have to be modified, fixed and tested if they require some code from a previous patch that didn't meet the manifesto
- Will people develop Dapps considering the ETC chain? Will the ETC chain have to manually merge any popular Dapps into their blockchain?
In short I don't believe that its going to be a trivial task to keep ETC up to date with changes from ETH. Even if ETC is updated to be equivalent, its still going to lag ETH.
This is assuming that most development and Dapps occurs on the ETH chain and not the ETC chain.