By this measure, John Harper's design of Agon 2nd ed is bad design, or Luke and Thor's design of Torchbearer 2e, given that all three would be well aware that there games would be more appealing if they were 5e D&D variants.Sure, and for a hobbyist making a game for just friends and family does make sense. But frankly not wanting to make as appealing a game as possible just seems like...bad design to me? The equivalent of making Plan 9 from Outer Space or something.
I regard this as a reductio on your inference to bad design.
4e D&D sparks joy (in me, and in others too). So do Agon 2e and Torchbearer 2e.Well, as has been established, "best" is subjective. The metric is: do users by and large like those things? Do they spark joy? If yes, then using them is good game design.
I can see the commercial benefit of sparking joy in more people. But I don't see how that is a metric for better design.