I think one thing people need to remember when they say thing like "th3/4/5/X give less additional effect than the first tier"- Virtually all job traits give more additional effect on the first level than the extra levels.

Meaning (example):
Store TP I gives +10 Store TP (Benefit over zero Store TP: +10)
Store TP II gives +15 Store TP (Benefit over Store TP I: +5)
Store tp III gives +20 Store TP (Benefit over Store TP II: +5)
... etc

So let's just make up some numbers here so people can understand the implication this has for treasure hunter. Let's just say TH I adds 1 to the percentage drop rate for items. Assuming Treasure Hunter increased in effectiveness in the same manner as other job traits, each additional tier of TH after the first would add only 0.5 to the drop percentages. You're still gaining effectiveness, just at a slower rate than the initial boost.

(Disclaimer: I'm not claiming that TH actually works as described above, I'm only using it to illustrate how additional job trait tiers go.)

That was a myth?
There are a lot of people claiming that you can get just as much increased treasure by having a sub THF as by having a main THF and that the extra boost from TH procs and higher level trait on THF doesn't make a difference. Thus, the community team is here to let you know that's BS and that more TH is always better.