Delay between real position and position on device

You won't get any better precision with Galileo.  Any lag is down to the time it takes the between your position being calculated and the map display updated.  These devices don't use really fast processors as they would be too battery hungry and in use the small amount of lag is acceptable.  Most people probably don't keep the map display visible either as it drains the battery more quickly and other metrics displays are more useful when riding.  I just have the map pop up at turns. I wouldn't really trust the Garmin to define dangerous turns either.

Sounds odd.  Map position and turn alerts on mine have little or no perceptible lag and cause no problems navigating a course, whether I'm displaying the map or only data fields.  This has been true since my first Garmin Edge 705 over 10 years ago and all subsequent units.  Back then it was GPS only but I use GPS/GLONASS now.  The Edge needs to have all satellite ephemeris data which can take a while to receive, but if you've gone for a ride in the clear, it should be all set.

Very odd. A difference of 30 seconds would make navigation completely useless. The time taken to process the gps signal on my edge, irrespective of which service I use, is so small as to not be noticeable. Not just with this one but all the various edge models back to the 500.

If you are having that much delay you have a serious problem and need to return your unit 

The OP may have got the lag time symbols wrong.  Up to a second seems plausible for lag - I see a little lag with mine.  As navigation prompts pop up 0.1 miles before the turn a second of lag doesn't matter.