Not trying belabor the point, but it depends on how you define what makes a switch heavy. Take a look at the two force curves below:
If you want to define heavy as the peak force that you must apply at any point, then the Box Royals are definitely heavier than Cherry MX Browns as there is a peak at the beginning on the force curve that is much higher than any point on the Cherry MX Brown curve. This is how heavy would be defined if you are thinking in terms of absolute strength needed, like in weightlifting if you keep adding weight on a bar until you can't lift the bar any more. Then the bar is too heavy.
I would contend that this is the wrong way to look at keyboard switch heaviness, because no functional switch ever made would be too heavy to push down, and you are never only pressing one key down and that's it (unless you are pressing the doomsday switch). Instead we should be looking at the total energy needed during each press. When you look at that value, you will see that the Box Royal energy over a single press is almost the same as the Cherry MX Brown (164 gfmm vs 166 gfmm). The energy needed to reach the actuation point is also similar (69 gfmm vs 73 gfmm), which matters if you aren't bottoming out each press. Think of this kind of heavy like pedaling an exercise bike. It's the work you have to do to make the pedal go one revolution that adds up over time tiring you out. I say that typing is a more similar activity to pedaling a bike, so the total energy during each press is what matters more. As a result, I would consider the Box Royals to be no more tiring to use than Cherry MX Browns.
I don't have a force curve for Zealios 67g switches, but based on how they feel, I think the shape of the curve is likely more similar to MX Browns, with a rounded tactile bump (albeit of a larger magnitude than MX Brown) over a large distance, and an even heavier pushback at the bottom. As a result, the Zealios 67g switches should actually feel heavier over time compared to the Box Royals although you are actually applying more force on the Box Royals than you ever are on the Zealios 67 g switches.
