First, the css rules are available on adguard as well. You can actually review the documentation here: https://kb.adguard.com/en/general/how-to-create-your-own-ad-...
Second, adguard is free. There are certain premium features, however. For instance, filtering ads outside of your browser requires a premium license. However, if you are comparing it to ublock this was already not a feature that was available to you.
Of course, even that comes with an addendum, which is that this is only something that you need to worry about on mobile devices. Should you be using the desktop version you will actually see that adguard is free and available here on github: https://github.com/AdguardTeam/AdGuardHome
In regards to pi-hole. The cumbersome nature of pi-hole makes it undesirable for me. There were many sites which were blocked for inexplicable reasons the last time I used a pi-hole and creating a whitelist for these sites requires more work than is necessary. First you must navigate to the portal, and then you must make changes to either the whitelist, or remove a site from the blacklist depending upon why the site is not accessible. It was not seamless design. However, those that find this feature desirable will find that adguard actually offers the same experience with adguard home: https://github.com/AdguardTeam/AdGuardHome
And as a matter of fact you will notice that there are comparisons between ublock origin available on the github page for your review. There are actually a number of features which are missing from ublock which are simply not possible with ublock origin. As for the accuracy of these features you’ll have to determine that on your own but you can review them here: https://i.imgur.com/5fSLuHx.png
Also, ublock origin does not marginally slow down a webpage rendering. It significantly slows down a webpage rendering. As evidenced here:
With ublock origin: https://i.imgur.com/4NxOysN.png
without ublock origin: https://i.imgur.com/jIlof5e.png
That means that when you are running ublock origin your browser is working at 87.85% capacity. Or in otherwords, a 13.15% decrease in speed. To put this in real world terms it would be similar to reducing the speed to 50mph* on a road that was originally 60mph.
So feel free to keep using ublock origin. As a matter of fact I also use it occasionally in a pinch. (It does, after all, significantly speed up rendering of some webpages. I find it especially useful on webmd.) However, for my daily driver I find it to be a poor solution.
*Rounded down, the actual number is 52.11.