I'd say a specific problem here, is the lack of definition of mediawiki platform. Mediawiki is too bloated to have a single team dealing with it all.
Topic on Talk:Wikimedia Platform Engineering/MediaWiki Platform team
More important than defining the team is to define its scope:
- Limits - What the team definitely is not responsible for and will not do
- Areas of responsability - What the team is directly responsible for and has VETO power.