Can somebody confirm this is working the same in the new version as it did in this thread? I have last login dates that are 6 to 9 months older than activity dates? Is there any chance a system activity or a admin user updating another users profile can cause an activity update trigger?

There is an exception not mentioned on this thread.  If you're an Admin using the User Switcher you can switch as that user impersonation, then as you navigate around the site that user's activity date will change, however their last login date will not.  I just did this now on my website.  I looked at one of the users having a last login date of 04/11/2018 and last activity date of 04/11/2018.  Went to User Switcher, switched as that user, then logged out.  Logged back in with my Admin accoount, checked the user I had impersonated saw that only the last activity date changed to 05/11/2018, while last login date had no change.