I agree with the article that the moral imperative of making the impeachment case airtight should outweigh the political difficulties of a protracted proceeding. If this is about a Constitutional duty, there should be no rush to judgment. Let's hear from ALL the witnesses, not just those hearsay and opinion witnesses who say things in favor of impeachment. Let White House counsel confront and cross-examine witnesses. Also, don't limit the time. If testimony of witnesses takes days or even weeks, so be it. This is a grave and serious matter which should be handled accordingly.
The standard of proof in a criminal case is "beyond a reasonable doubt ". I would argue that impeachment should rise at least to that level, and perhaps a wee bit more. After all, this is not just the fate of one man's freedom, but goes to the core of democracy. In this situation, it's important to get a vast majority of the American people on board at an overwhelming rate and not just 50% + 1. Polling data is not there, so there's work to be done.
I am confident that Schiff and Nadler are the capable "truth seekers" that can make the airtight case in a process seen as "fair". To get there, they do need to expand the scope, allow WH participation and let all witnesses - whether or not those witnesses would tend to convict - be heard. Otherwise it will be seen as a rush to judgment and a sham. In the words of Adam Schiff, they "can do better than that."