How big a deal? About the biggest.
It's important to notice the difference between this and a criminal or civil trial. The fundamental point is that it is investigative and is trying to recommend improvements - thus the witnesses are there to inform the enquiry.
Normal rules of evidence don't apply, thus witnesses can provide hearsay, opinion, etc, without representing counsel being able to object to questions. Documents can be 'called for' by the RC. Notice how HHJ McClelland responded to the WT lawyer's request not to introduce the whole of a particular 'confidential' manual into public evidence - and how he asked questions about selective implementation of bible texts.
There is no jury to impress, nor any need to. It has been established that the Aus head branch committee guy gave false and misleading instructions to the WT lawyer. Established beyond doubt (but without drama) to the extent that the lawyer apologised to HHJ and said that he had not personally sought to deceive or mislead. In court-type language this is the equivalent of admitting that his client (branch head honcho) told him lies.
Similarly, when HHJ commented that a consultant's certificate concerning the health of Jackson's father may not necessarily assist, this may be taken to mean that HHJ has lost patience and a summons will be issued. (Practically, the lawyers for WT may be asked to accept service and will do so).
In a jury trial, CA Mr Stewart would probably have pursued the 'misleading instructions' part further and asked who had been consulted by the Aus branch guy. (Does anyone doubt that he was on the phone to the GB?). But here, no need.
It's cut through the crap obfuscation between the Aus branch committee and the legal Aus WT corporation (in a couple of questions). And where the real power in JW land lies (GB) and that there is no deviation from it. And in at least one Aus state, failure on the part of anybody to report crime (s.316) is a crime. Oh, and the 'list'.
Outcomes? Well, we already know that the WT must shortly produce a submission as to where its policies are wrong and harmful and how it will change them. And that by the end of the RC in a couple of years, how those changes have been implemented. (Including, possibly, how women will be involved in decision-making roles). We know that the RC is contemplating a 'redress organisation' for victims, funded by all organisations/institutions involved. And that the RC is not going away.
In colloquial terms for the JW leader witnesses before the RC, you may have had a shit day in court but it's only going to get worse.
I can see that for some viewers (esp. our US friends) this might all seem a bit tame. But it's being done politely, determinedly, and with superb research. No need for drama. This works better.