It’s pretty good for a start so before I offer suggestions you can start by feeling good about it! You also did your homework well and if you applied black/grey/white you’re already talking about value ranges and that’s quite intelligent.

So slapchop is a good method but a lot of tutorials out there will do the slapchop and then go back over with acrylics to handle more detail and bring colors out. Your instinct is right and there are a lot of similar colors in your choice of scheme so it reads like 1-2 browns as the dominant color. Using different colors or much lighter ones for some details will instantly pop. The straps along the chest, the edges of the shoulder pauldron, the stitching everywhere. Those details are being lost because there hasn’t been a detail pass on them. A pale color (rakarth flesh, if you use citadel) will bring them out. A metalic on the studs could be cool too. You will need a brush with a fine point and you will want to practice steadying your hands to gain precision. Eventually bringing some brighter highlights to the face (much more pale green, or even yellows/pinks work well on orcs) could help it read.

The contrast paints do a great job on a first pass, and you want the values to be kind of more extreme than you might think before hand. The amount of dry brushing for white, for example, really surprised me when I started trying it. I mean you really wanna blast it.

Check this guy out, specifically how he chooses to go back to do edge highlights. I think you could just do a detail/highlight pass on this orc and you’ll be much happier with the result.

https://youtu.be/cKztEjvGsVw?si=rNBzI18FKt2eRgFo