Winner/error ratios aren't highly reliable, for a number of reasons.
For one, UE's aren't assessed in a consistent manner. What's called a UE in one match isn't in another. Some counts are way off the mark. The worst I've ever seen was a match in which the UE total was inflated by a factor of 12!
Another reason is that UEs aren't the only kinds of errors. In addition to forced errors, there are also tactical errors and execution errors. I've seen many matches which are loaded with the latter two, which were really poorly played matches, but they came up quite "clean" on the stats sheet.
And there are the errors themselves. The UE stat equates a shot that just missed the line, or clipped the tape, with one that's sent into the next court. That's hardly the same. Plus, the stats don't tell you when the errors occured. Was it on the 3rd stroke? The 10th? The 20th? And it doesn't measure the quality of the rallies. If two really fast players are facing off, there are often several spectacular shots that should be winners, which are returned into play. Thus, even if the point ends in a UE, in order to assess the quality of the match, you'd have to treat it as if there were a couple of winners hit as well.
Which underscores what the posters above were saying. You really have to see the match to be sure. The stats are no more absolute than the scorelines. I've seen 6-1 and even 6-0 sets that were dead even, and 6-4 sets that weren't competitive at all.