The use of complete on-drawing history is useful when the controlling company has only the master print, keeps no history prints, and wants no other paper to search for.
As they are mainly used I agree that the ECR/ECN process is to get all affected parties to a unified understanding of changes they need to make now.
Sometimes the reason for revision is handy when figuring out why a product changed performance and one can look and see that a specific problem was addressed and maybe a searchable database of those could be used if a similar problem arises elsewhere and the old guy who cane up with the original fix is retired or dead.
Also, I am a proponent of using a Wiki for all product development which would record all the relevant discussions, test reports, proposals, reasons for accepting or rejecting proposed solutions, the entire drawing history from scanned napkins forward. This rather than or in addition to a typical PDM system. If Wikis had an approval system then even the PDM system would not be required.