App Store blockers can be and in some cases are as efficient as uBlock Origin. Many are likely more efficient as the blocking is implemented directly by Safari using optimised content blocking rules that are executed by native code (as opposed to Javascript execution as per UBlock Origin).
When compiling the content blocking rules, Safari also ensures the rules fit within reasonable execution limits to ensure there is absolutely no speed decrease due to blocking. If the rules are excessive, they are rejected by Safari.
In terms of effectiveness, yes there is variability between different blockers. We are the creators of one blocker for iOS and Mac and have found that it is extremely effective and in tests we've done provides a 2x speed-up on web page loading and rendering speed (for the top news and media sites we tested)
https://www.magiclasso.co/insights/difference-adblocking/