>>9562147>mid-gameThe MC Iron pickaxe allows you to mine everything in the Overworld except obsidian, a material you almost always find close to lava. You need to go through 2 tiers of pickaxes before you can make that one. You find plenty of ore by exploring caves.
The Terraria Platinum and Gold Pickaxes (same tier) allow you to mine everything in pre-hardmode world except hellstone, a material you almost always find close to lava. You need 1 pickaxe to get there and you're spawning with it. You find plenty of the required ore by exploring caves.
>unless you dig extremely deep downWrong, Terraria's underground is just deep enough that the surface is out of vision.
>then you cannot mine it without going through several tiers of other ores.Wrong, see above. If I were to autistically take you by word that mid-tier is what you can achieve in 2 pickaxes, you even get a few bossfights into hardmode on Molten armor. Before the last content patch, you could get there in one (1) just by fishing.
I have no other explanation for your statements other than you not knowing what you are talking about and thus having no idea what mid-game in both games even means.
The difference is difficulty, and that's a matter of subjective preference, not objective accessibility 
