I've only run campaigns in two systems since 2014 (though I've run a number of one shots in other systems): D&D 5e and Warhammer Fantasy Role Play 4e (WFRP4e).
DnD 5e is simple and probably doesn't warrant much attention in this thread. Though, I will say, that moving to DnD Beyond made things much easier. Leveling mostly takes place between sessions. Players do it themselves and I can easily look over in DDB. DDB makes it easy for players to avoid mistakes. The only time it gets complicated is witch homebrew stuff. But that's on me. If I'm going to inject homebrew rules, I need to create the options in DDB and test them on character sheets.
For WFRP4e, I wouldn't be running it if it were not for the excellent game system Cubicle7 sells for Foundry. Still, I did have to step the players through the character builder and character sheet. We spent most of a session just building characters and testing making rolls and applying conditions, etc. This is the also the first time since 2014 when we done all leveling in session. Even with the Foundry character sheet, WFRP4e is a lot more fiddly and crunchy than 5e. Also the rules are spread across so many books, with many replacing the rules in the core, rather than just being additive. Foundry helps with that a lot with the search, cross-reference links, and some logic coded in the character sheet, but I it is a lot more taxing on me as a GM than 5e.
But now that we are over 16 hours of play time into the campaign, it is getting easier.
One of the players is really into the rules and has the books he needs which helps a lot. Not only in that he knows his character sheet and the rules pertaining to his character, but he can help the other players, taking some of the burden off of me.
I don't demand that the players buy the books and study the rules. They have access to all rules content in Foundry. If I had demanded they learn the rules, we'd still be playing 5e. Instead, for the first 24 hours of play we are playing through the starter set adventure, which is run kinda like a video game's tutorial mode. It starts out very railroady, stepping the group through different situations that introduce them to various aspects of play, feeding new rules slowly. It gets less railroady near the end. After we complete this adventure, we'll start the campaign proper.
I feel that this works very well for a crunchier system like WFRP. While most of the players are not developing anything approaching rules mastery, they do know their characters well and the core rules of game play.
Another thing I find important with crunchier games is having a frank conversation with players who are not into spending much time on understanding complex rules and suggesting they play less complex characters. Many players fall into the trap of wanting to play spell casters but getting overwhelmed by the options and slowing down the game. For players who don't want to their character concepts to be limited, but also have little patience for complex rules and options, it might be better to play a different, more narrative, game system.