I really enjoy the way black desert did their skill and combo system. So much better than slotting abilities on a hot bar. Everything should yield decent experience. Leveling by combat should not be the only option. Small, match made, mini dungeons while leveling are a lot of fun. Lower levels having a tank shouldn't matter. The more of those the better. One of my favorite things in an mmo was in Star Wars galaxies. Gathering materials was above and beyond any other game. You would prospect areas for different materials that were finite. Material grade was important for some crafting. When one material would be depleted, another would take its spot. When you found a good material you would plop down all of your harvesters and go to town. A harvester made with high quality materials would work faster and more efficient. There was an entire site mostly run by the community that would let you know all the resources for all the servers and their quality. That last bit I mentioned made it the most enjoyable mmo I have ever played.