By looking at the previous logic, I think this update option only triggers when if ( false === get_option( 'sensei_installed', false ) ) is true. Do you think it make sense to move inside the if statement so it wont trigger on each plugin activation?

On the contrary, that's precisely how it works, only on the first installation and not on each activation.

Sorry, I probably didn't explain it well. Here's a quick clip of what I mean:

With the current logic, the update_option( 'sensei_installed', 1 ) is always called when the plugin is activated. By moving that code inside the if statement, this database call should be avoided. By looking at the previous logic, this is how it worked before, but it used a somewhat confusing return call to prevent the update_options call. Does it make sense?

Ouch, you were precise enough. I misunderstood it.
It makes sense; I'll move it to be part of the if block.