I have been building character sheets for Heroes By Trade. This is a tremendously useful exercise because it gives me information on just how complicated I have made the rules. I remember building characters in Pathfinder and being amazed at how many numbers went into each calculation. Armour Class seems like a simple concept until you see it broken down into three categories of AC - touch, regular, and flat footed, and then you see the huge list of different things that modify each one. The calculation of defence values and hit rolls in HBT is drastically simpler than in Pathfinder (which, in fact, was one of the defining reasons to build the system in the first place) but I do have an additional wrinkle in that every character has a soak value for both physical and magical damage.
People have found that last detail a bit of a challenge and there has been a lot of desperately searching character sheets for the appropriate soak value for the incoming damage. I know that HBT is much simpler than Pathfinder but it is tricky for me to decide if it is simple enough. I want complex tactical decisions but I really want a game that people can figure out the numbers very quickly. The question "What happens if I do this?" should be trivial to answer and the question "What is the best action to take?" should be very complicated. People get those messed up a lot and miss that many games that are deadly complex to understand consistently boil down to a single best strategy. Getting perspective on this is difficult as I am so much inside the system myself and knowing what every number does is intuitive. People other than me on the other hand don't seem to find it as straightforward as that.
I could simply have a single avoidance stat and a single soaking stat rather than having both of them for physical and magical damage. This would make things simpler for sure but would lose some depth of strategy. Some characters and monsters end up much more vulnerable to one sort of attack or the other and it is interesting to have to figure out who should be attacking what based on those vulnerabilities. There is nothing generally wrong with just having Dodge and Armour but sometimes having Dodge, Armour, Ward, and Resist lets the players be clever and send their physical tank to go tie up the ogre while the magical tank engages the enemy necromancer and that feels pretty great. It also lets people be differentiated somewhat and feel like their stat spreads really matter.
I do have the issue that there is a cost to adopting a new game. Even if DnD is more complicated it contains familiar mechanics that people will easily fall into because they have seen them before - in order to really be appealing I need HBT to be significantly simpler while simultaneously being tactically superior. DnD designers do have the constraint that they have to cater to the nostalgia of the grognards but having said grognards around does have big advantages in terms how much complexity can be crammed in.