you can’t compare the situation of the early days with today. In the early days, you really could change definitions of “important” tags and nobody might notice for a long time (and most tags weren’t codified anyway and were difficult to find because templates were used to a lesser extent), today there are many eyes on the wiki and if you make important changes to tags in significant use without consultation, chances are high it will get reverted if it is disputed. To give an example, say someone operates a business which has vital interest in some cyclespecific tags, I would expect them to monitor the relevant pages and raise the issue if someone makes dubious edits to these definitions.
Regarding your example of the barrier-tag “default”, I do not have the impression this general “no”-definition has stuck, so somehow it did work out and things have been fixed. It may have been timeconsuming to find an agreement and document it, as discussing things is always more onerous compared to having a hierarchy of a few decision makers who decide for everybody and no questions taken, but the hope is that the result is more appropriate for our setting and values.