You're mistaken on the synth achievment, you are nowhere close to being complete by the time you hit 50.

My Goldsmith stands at 45 starting from 20 with the achievement and my stats are as Followed
1-10::0/50
11-20:3/300
21-30:218/750
31-40:87/1500
41-50:207/3000

So ya, by the time I hit 50 maybe I'll be at 300-400 but still nowhere near close to getting a tool. Synth wise the penalty comes from finding a recipe, spending gil and using crystals to produce the synth. Gatherers don't have to do this to them the achievement can be pure profit. With recent changes to crafting one can get 120 synths done about an hr with hasty hands so that's about 47hrs of crafting.

For gatherers it's about 18 trees are hr maybe more so 144 cuts an hr. So maybe about 152-155hrs(including travel time between nodes) to get it done, so three times as long but it's pretty much all profit you don't have to make any investments when doing this achievement meanwhile with crafting you do have to spend gil or gather it yourself/spend time before you can actually work on it.

But ya it's really to each their own, achievements have that easy/normal/hard sense to them in obtaining them which can vary from skilling to time required to achieve it. Those 100mil and 100k leves are perfect examples. If everyone was able to get every achievement then what would be the point of having an achievement system. The system is made to have something for everyone and have people decide what they would like to achieve. So if you find certain achievements to be to daunting just ignore them lol.