Yes, I can clearly (hah) see a difference between those two snaps, and the iFly image is far lower-res. Something is not right...that is *not* how the maps render for me. Pixellization is not apparent on sectionals for me until I am zoomed several levels closer in than your screenshots.
I will say that you are correct regarding the approach plates not being PDFs. I'm not sure why that is, but I suspect it may be a legacy compatibility issue. iFly started out on a custom WinCE platform, and I suspect that embeddded PDF support may have been hard to implement in that device. Regardless, even though "infinite zoom" (like you can do with most PDFs) is not possible, again the resolution of those files is quite high, and pixellization is not really apparent until zoomed in farther than there's any practical need.
Here are examples of what various zooms look like for me, both for the sectional view and for an approach plate. (I tried to duplicate your zoom level, but couldn't get it exact, so took the next closer zoom level, then another shot four zoom levels further in.) The link takes you to a thumbnail, but click on the image and it will expand to full resolution.
KDYT comparable zoom: https://imgur.com/Co0RsGw
KDYT tight zoom: https://imgur.com/anQljSg
Approach plate tight zoom: https://imgur.com/DIDxGZ2
Approach plate tighter zoom: https://imgur.com/B5EZxGW
Note: These screenshots were taken from a Windows PC running at 3200x1800 resolution (it's what I had handy at the time), but there's comparable clarity on my Android tablets at 2048x1536 (which is equivalent to iPad mini resolution and not too far off from the 10.5" iPad Pro's 2224x1668).