Oh, excellent! The plan for Riigikogu members is to migrate everyone to the "member of the Nth Riigikogu" approach, rather than the current mess (which is actually worse than your list, as there's still a bunch of people using P463 as well). That has stalled a little at the moment whilst we investigate the new Parliament API to see if that's suitable for getting well structured data for this, rather than the quite painstaking work required to construct that information for previous periods, but I'm hoping we can get at least some more of that done in the next week or two. There has been discussion of an event quite soon to do a lot more work on this (though probably in Tallinn) — I'll let you know when anything more is decided on that.
You might also find Wikidata:WikiProject every politician/Estonia useful/interesting, and also Wikidata:WikiProject every politician/Estonia/Q2421589/positions and the list pages linked from the final column of that. I've been slowly trying to tidy some of this data up, but again that's quite a painstaking process, and it might be better getting confirmation that the information at https://www.valitsus.ee/ can be treated as open data suitable for bulk import.
The only sub-national work I've done previously is a little bit of tidying of some of the mayors.
Definitely very happy to help out tidying things up more.