I have performed QA tasks on both, and find that either JS developers are better or going pure vanilla makes a much stabler product. The TypeScript projects I have seen had some major flaws and requests (vs bugs) always turned into low priority because of the inability to perform the task.
I think it's easy to explain: TypeScript is a new technology and programmers will have very little experience in using it. It's completely impossible to find "TypeScript programmer with 5 years of experience" for example. On the other hand, JS is stable and much older and you can easily assemble a team of highly experienced people.
Relative strengths and weaknesses of TypeScript will be only visible after it's around long enough to get its own best practices and experienced programmers. I see the same process with CoffeeScript - in the beginning average CS code was much worse than average JS, but now they are comparable and the advantages of CS are starting to be visible.
That's of course on average. It's still possible to get a few people with enough knowledge to be able to use TS effectively, but I think it's hard enough to make it very rare. It's unfortunate, but technologies - and especially languages - take very long time to mature. In short, your impression is probably correct, but it's not because of TypeScript features; we need to wait a few years before we can compare TS and JS products success rates.
