NOT at all impressed with the implementation of this in SP 26! You definitely didn't take my 2019 suggestion below to have it go the other way. You have a constraint if the edit comes from the relationship side, but edits on the job side can keep the dates out of sync. Additionally, since this is a new constraint, we have data already in the system that doesn't conform to the constraint. While QA-ing the SP, I discovered that a user could inadvertently update the job dates if they were editing the relationship for any reason. The user can also run up against an ugly constraint error if they edit the relationship and the end date is before the last job's start date. (This can occur due to prior unconstrained data or a user updating the job date without updating the relationship date.) This has created a great deal of work for us to compensate for this feature that is touted to help with our data integrity, including my QA time, as well as developer time to customize the job forms and try to clean up the old data accurately.

Released in SP26

Planned for SP26

It would be nice if this went the other way around also... If the employer relationship already has an end date and you add a new job title, the relationship end date should be removed. There is a great deal of messy non-synced data in our system because of this, and I'm having difficulty finding easy ways to fix the errors programmatically, when this should be a system function.

Please add this functionality!

Agreed, this is a no brainer!

Career level needs to be added to the Relationships section and not be a separate piece in Employment history.  Any step out of sync with the original process is easily forgotten by updaters. 

This is just a best practice issue, I don't know why this has not been set up before, this really needs to be set up.