I'm not sure what you mean by short-term trailing results of VTIAX vs VTSAX. The fundamentals of intl equities are good, but will I put money into VTIAX when it shows -7% of stock value over 10 past years? or total 1.5k growth with dividends of 10k in 5 years? Probably not.
What I mean is that the previous returns of any fund I don't already own are completely irrelevant; the only thing that matters is what I expect it to do in the future. And by "future" I mean 20 - 50 years from now, not 5.* Given that I expect the developing world's economy to eventually catch up to the US's (which implies that theirs would be growing faster), that makes international a better buy.
But the real issue is that even if I didn't think it was going to do better, I'd
still buy it because I don't know the future and could benefit from the diversification. (A true, cap-weighted total stock market portfolio is something like 45% international; the 100% VTSAX I had before was an
extreme US tilt.
Some US tilt is appropriate since I live here and invest dollars, but not that much!) Even if I thought VTSAX would do better in the long term, I don't want to take that much risk of being wrong.
The bottom line is that a 7% drop just before I buy a fund is not even slightly something to be concerned about. It just means I get more shares for less money, and that's a
good thing!
In contrast, your strategy -- to buy VTSAX because it's expensive, and avoid buying VTIAX because it's cheap -- is exactly the opposite of what you should do. It's the epitome of "buy high, sell low." (Of course, by "expensive" and "cheap" I'm really talking more about PE ratio and whatnot than current price vs. past price, but I digress...)
(* Even if my FIRE date is sooner -- I'm aiming for 10-15 years from now -- it's not as if I plan to switch to a 100% cash portfolio on that date, so my time horizon is still much longer.)