Breh you discovered a secret of the work world. The higher up you go, the more power you have, which means less people to answer to, more people to delegate work to, and the easier work is. Plus you get to take credit for all that shyt.
This is mostly true. I got promoted last year. I worked MUCH harder in my previous job (though, the previous steps on the ladder were not as hard) than I do now.
Bascially, i used to have to perform regular work tasks, then develop the business processes/rules required to complete them, and explain them to people. Got promoted to a completely different section -- now, I write the business rules and processes for the regular work tasks that other people do (those people don't work for me). Still writing/presenting/explaining ... but that's my daily work now, instead of the shyt ON TOP OF my daily work.
BUT, I've certainly noticed that my boss (where I'll be with one promotion) knows much more than i do, and also works harder. So, basically, I'm good for now. Not interested in the next level until my kids are old, or I become ambitious or something.
Long story short -- put in effort. But put in the RIGHT EFFORT. Grinding for its own sake (sold to us as "work ethic") is bad business. Make sure your work is leading you somewhere you want to be. If it isn't, find some work that will, and work hard at that.