Navigating to a saved location on a Garmin Edge 530 results in a ludicrous circuitous route
My guess is that &quot;popularity routing&quot; is weighted quite heavily in the choice of route, and &quot;minimise time&quot;  is a secondary weighting.
I see Google has routed you on the A541, which  is definitely more direct, but may be less &quot;compatible&quot; with cyclists and therefore less popular.  The Strava route has used B5429 which is even narrower, but seems to have less traffic, based on Street View.
Strava and presumably Garmin can access their pool of data about where people ride.  I'd posit that the climb out of Y Groes Fawr is rather popular, having 200 metres hard climb after a 100 metre of more-gentle climb.  That's the kind of effort where pacing is critical, and it sorts the rabbits from the tortoises (the go-hard-and-blowers from the pacers)  Specifically https://www.strava.com/segments/6671074 the Moel Arthur climb.
Putting that to the test - here's strava's heat map showing both google and your routes.

Visually you can see that the Strava route highlighted in Blue is brighter than the other three google routes, so while people do ride all those paths, the one you rode is more travelled by Strava users.
My first version of this had bright magenta for the google highlight, and it seriously obscured the point.  The green and blue are chosen to both have similar low luminosity levels.  So ignore any stray hot-pink dots please.
Search around more at https://www.strava.com/heatmap#12.14/-3.32479/53.25998/bluered/ride  and see how the results match your personal experiences - the good riding roads should be more-ridden than the horrid roads.