And you seem to fail to understand the meaning of statistical sample sizes.

For example, suppose that TH9 gave a 20% drop rate on an item, and TH10 gave a 25% drop rate (pretty substantial for only an extra +1 proc when you're already starting at 9). Would you consider that a significant increase in drop rate, implying a significant value in going from TH9 to TH10? I think most people would.

However, 500 kills for each TH level is not enough to statistically separate those two values. 1000 kills is not enough. You'd need about 4000 kills to statistically distinguish a full 5% increase in drop rate (a 25% increase in drops received), and even then all you know is that TH10 > TH9; you still couldn't really be certain of how much of a difference there is.

Your complaint that you need thousands of kills to be sure of a difference between the two TH levels is merely a reflection of someone who doesn't understand statistics. You will *always* need thousands of samples to get any kind of decent understanding of the underlying rates of anything in a game like this. You can only get away from it if you're dealing with data that you know is discreet and precisely repeatable, such as exact haste or enmity values.



Now, to take things further aside:

I've read one bit of testing which implied that TH1 was a 50% increase in drop rate over baseline, TH2 was an additional 50%, and each additional point of TH above that was +10% (a fairly reasonable model, really; I'd like to try testing to confirm it). So, TH9 would be 50%+50% + 7*10% = +170% (and TH10 would be +180%), or 2.7x the baseline drop rate. If the original drop rate was 10%, that means you'd have a 27% drop rate with TH9 and 28% drop rate with TH10.

To distinguish between TH9 and TH10 in that model you'd need about 25,000 samples to reach a margin of error small enough to be reasonably certain of your results, though a few thousand samples at each of multiple points to create a trend line would probably be more useful.

In such a hypothetical model, the 50% tiers would be:
TH0 - baseline
TH1 - +50%
TH2 - +50%
TH7 - +50%
TH12 - +50%

A main thf and a single TH proc (TH7 total) would be the equivalent of an additional 50% TH tier, which is decent, though not exceptional. Since you're already 100% over baseline with TH2, it would be a 25% boost in the number of drops received over what you could get from a /thf. That would not be terribly out of line with the general feeling of the gain from bringing a thf main compared to a /thf mule.

The data for this model was taken from before the level cap raise, though, so there's the potential that the third TH trait thf natively gets could be another +50%, with each TH+1 from gear or procs being +10%. That would make TH7 +190% instead of +150%, and would give 45% more drops than a /thf.