Do you have a flat tappet engine or a roller tappet engine? I seem to recall Camguard is not the same as the tri-cresyl-phosphate additive Lycoming specifies for flat tappet engines...here designated by Shell as "Plus".
https://www.lycoming.com/sites/default/files/Lycoming Engine PN LW-16702, Oil Additive.pdf
I do not wish to steer the conversation toward a Camguard debate, only note a difference between the oils.
Oil darkening (dirty oil, as described) indicates suspension of contaminates...carbon, metallic ash, lead salts, etc. You've viewing the dark oil as being caused by some change in piston ring sealing. It is absolutely true that an engine with greater combustion gas ring leakage will darken oil sooner. However, absent a good physical reason for a change in ring sealing, we might consider an alternate view, which is that one oil suspends contaminates better than the the other.
For sure there is one
major difference between the compared oils. Aeroshell W100 Plus is a single weight oil, while the Phillips is a multigrade. When
cold, the Aeroshell will be much thicker. When hot, viscosity will be similar.
I'd suggest the consumption difference is entirely based on low temperature operation in the early minutes of each use. When the W100 oil is thick, the rings (notably the oil scrapers) remove less of it from the cylinder walls on the downstroke. More is present on the cylinder walls during the combustion process, where it is heated, thinned, and scrapped off the walls by the top ring during the upstroke.
The theory may be tested. Use Aeroshell 15-50 for your next oil change cycle. See if consumption is reduced with another multigrade.