Terve!
You are advised to check this changeset, which you may accept or reject asap since it will be harder to revert as time goes by.
(The very enthusiastic user (Miro | OpenStreetMap) have started breaking admin_levels of various countries and most of those already have been reverted.)
By the way it may help if you could talk to your fellow Finn to help him to understand the problems he have caused Europe wide. 
Since I’m quite a noob as someone might say, I don’t exactly know what he has done, but maakunta is one of the top level regional administrative areas in Finland. I think choosing it as the highest level makes the most sense in OSM, because it’s the one displayed on traffic signs. Before there was many confusing boundaries, some which were statistical boundaries and some I think were NUTS boundaries.
In my opinion if he hasn’t broken anything else, it’s an improvement.
och samma pĂĄ finska:
Koska olen, kuten joku voisi sanoa, aika aloittelija, en tarkalleen tiedä mitä hän on tehnyt, mutta maakunta on yksi Suomen ylimmistä aluehallinnon tasoista. Mielestäni sen valitseminen korkeimmaksi tasoksi OSM:ään on järkevämpi, koska se on se, joka näkyy liikennemerkeissä. Aiemmin siellä oli monia sekavia rajoja, joista osa oli tilastollisia rajoja ja osa taisi olla NUTS-rajoja.
Jos hän ei ole rikkonut mitään muuta, mielestäni tämä on parannus.
Well, they did do a Request for Comments on such an automatic edit in the Finnish section of the Forum (and waited for comments that didn’t materialize), which I think is the way to go.
I don’t know whether they have repeated such a request in the other fora, but I’d say that automatically editing administrative boundaries of multiple countries throughout Europe (particularly if they haven’t asked the local communities for comments first) is at best very bad form, and at worst could be construed as vandalism.
But, yeah. If people here think that there are problems with the edits in the Finnish admin levels, they can raise their objections in the other thread I linked to, and hash things out there.
In his changeset comment and in his forum message to the old thread regarding other boundaries, he justifies this change because a lower value of the admin_level key makes the boundaries appear on lower zoom levels. This could be seen as mapping for the renderer which is discouraged.
In his forum message, he also brought up that, e.g., the provinces of Sweden are at admin_level=4 and we should follow them. I have to state that the Swedish provinces have a level of autonomy, including the right to collect taxes and an elected council. Russian federal subjects, American states and the Norwegian provinces are also more or less autonomous. Finnish regions (maakunnat) do not have this kind of authority themselves but work as an area of operations for other agencies. Also, Estonia and Iceland, for example, lack admin_level=4 boundaries.
I would highly appreciate it if these kinds of edits were made not on the basis of what looks good and only after consulting and getting the approval of the local community. I have not yet looked up what has been done in other countries.
Because of matters mentioned above I would propose the edit to be reverted to allow further discussion on reasons why the change is needed in Finland, if it is.
This fact supports using admin_level=6, and comparing the wiki table [1] it is clear that level 4 is mostly used for regions that have some degree of autonomy. In addition to the ones you mentioned, for example Germany has states, Spain has autonomous communities etc.
There isn’t many countries with no admin level 4, but that isn’t a reason to use it.
Wiki doesn’t really state what admin levels should be used for what, but the article key:admin_level has few hints. There’s mentions: While admin_level=2 is almost always a de-facto independent country, and admin_level=4 is usually equivalent to a "province", higher values vary in meaning between countries.
and
admin_level=4 (sub-national jurisdiction)
So I vote for Maakunnat as admin level 6 (unless they gain some degree of autonomy and tax collecting rights 
)
As a side note the wiki table should udpated for Finland, once we reach a mutual opinion here.