In DF I remade night troll's grinding vermins into paste as reaction usable by player, that taked few hours of testing and some minutes for writing (I mean all changing in raws). In RA2 I remade Forgotten from TS by few days.
Ah, I see. You figured out how to edit game data text files and now you think all modding works like that. Editing game data text files is incredibly easy. If any of the mod ideas you posted required only editing such files, I would have said "one hour or so" in my estimate. But I said stuff like "a year" and "six months", and there's a very good reason for that: your ideas cannot be implemented just by changing data files. All your ideas have some aspect to them that would require writing some Java code. Now here's the deal: writing Java code that makes Minecraft properly do what you want it to do is much much harder and slower than just messing with some data files, especially since Minecraft was not written with mods in mind, just like the skyscraper from my analogy wasn't built on rails.
Consider the Baubles mod, which does something very similar to the four-layer armor thing you suggested. Read through its
several thousand lines of source code and commit history and tell me how anyone could write, test and bugfix that mod in under three months.
Here's another analogy until you get the point: If you went to the car repair shop and asked the mechanic "hey can you change my tires" he'd say "yeah sure, come back tomorrow and I'll be done, tires are designed to be easily replaceable". If instead you asked the mechanic "hey can you make it so my car can drive underwater," he'd start telling you why that's incredibly difficult for a large amount of reasons, and that you can't just quickly replace some car bits with submarine bits and add some duct tape. And you know what? The mechanic would be correct. He knows a lot about cars, more than you. You should believe the mechanic.