> Actual transit providers typically lack the technical knowledge
This is actually getting better, as most of the transit providers already rely on software companies that provide their own route planning software for passengers and/or administrative software like tools to create the actual schedule with. These companies are slowly getting better in providing standardized feeds.
I am skeptical that something like a feed-wiki would work, both because of vandalism, and because schedules are usually incredibly complex. You may have noticed that your bus starting at 14:30 from station X was scheduled incorrectly, but does this service has this mistake every day? What about the 3 days a year where this bus has a slightly different schedule? If the bus travels every 5 minutes, and each trip has this mistake, you have to manually check hundreds of trips per day if they contain this mistake. Automation is difficult here, because trips that occur frequently are very often not grouped by any mechanism (although for example GTFS provides such mechanisms).
I think the better way is a legislative change which requires all transit companies to submit their schedule data to a central authority, which then publishes the merged schedule.
There is now (since the beginning of 2020) a new EU regulation [0] which basically pushes for an EU-wide multimodal route planner and schedule dataset (published in a special format, NeTEx). This makes it now possible to rely on the data of existing national schedule aggregators, which have been checking and merging timetables of all national transit providers for decades. For example, in Switzerland, the national railway company SBB does this (GTFS feed published here [1]), in Austria its also the national railway company ÖBB, and in Germany, its Deutsche Bahn (GTFS feed published here [2]).
[0] https://eur-lex.europa.eu/eli/reg_del/2017/1926/oj
[1] https://gtfs.geops.ch/
[2] https://gtfs.de