Most structures pre-1.13 absolutely suck (especially the Woodland Mansion, by far the worst structure in the game). Luckily, post-1.13 structure design is actually pretty darn good lmao
OP loot datapacks take next to no time to make. Replacing a single loot table with OP items and packaging it in datapack format takes at most 15 minutes. There are people who spend tens, even hundreds of hours on high quality datapacks. And what do you do to get levels (which don't even matter)? Upload crappy OP loot datapacks.
Yes, there's a block for Light. You can check the wiki, it's pretty useful for mapmakers.
A light block with a light level of 0 is entirely useless as it doesn't produce any light (and it doesn't stop light), getting rid of its one actual function.