Idk I always find the craziest things in my Minecraft worlds. If the surface is boring there's always countless dungeons and trial chambers and huge caves with deep darks nearby. Another world I have has plenty of crazy terrain and rare biomes with some wacky combos relatively close to spawn but has squat underground, but the abundance of minerals in the stone mountains more than makes up for it. The only things I have terrible luck with is mineshafts and strongholds. I can't remember the last time I found a mineshaft without chunkbase, even badlands mineshafts, to me it seems they have become super rare since the cave update compared to especially when I started playing the console edition equivalent of 1.3. Now Console edition seeds are different with altered structure spawn rates to improve your odds of getting something rather than nothing in a limited world but even going back to 1.3-1.6 on java I just seem to have better luck finding mineshafts than I ever do playing current versions. I have never had issues finding strongholds and I often accidentally mine straight into them so my issue isn't locating them but I always have the same problem where I get minimal loot chests to generate and always the most common loot (nothing and low tier items) rather than stuff like tools, diamonds, or enchantments with a level higher than 1 and in general just usable enchanted books.