Well, you are involving some facts like technology, I mean the DS is almost 20 years old, it would be like saying original Doom is worse than Doom 2016.
Letting that aside, yes I completely agree with the dpad, it can be tiring with long sessions.
Also I am aware that you play with the thumb, have you considered to play the games with something like this I luckily own one and since my touchscreen was replaced it is from a worse quality so touch inputs require a lot more force with the thumb, with something like this thumb inputs are nice, I could even attempt to play your way with this haha.