DNA Land seems to be very accurate for Poles and mostly in line with 23andMe.
In my graph Davidski is Pole number "14".
Davidski in DNA Land has 80% North Slavic, 10% Balkan, 10% North-West Euro. I haven't seen his 23andMe but you told me that he scores 90% Eastern European. DNA Land seems to be more accurate for him, considering what is his ancestry (he is a mix of Baltic Poles and Western Poles - and I assume that his Baltic Polish ancestors would be scoring 100% North Slavic and 100% Eastern European).
Now some Latvian and Belarusian results (but not from 23andMe):
Here are Latvian FTDNA MyOrigins, Geno 2.0 NG and DNA Land results:
100% Eastern European
100% Eastern European
96% Eastern Europe + 2% Finland & Northern Siberia
98% Eastern European + 2% Finnish & Siberian (DNA Land - 100% North Slavic)
88% Eastern Europe + 12% Finland & Northern Siberia (DNA Land - 92% North Slavic, 2.1% Ambiguous Northeast European, 5.2% Northwest European, 1.2% Ambiguous)
89% Eastern European + 11% Finnish & Siberian (DNA Land - 100% North Slavic)
Interestingly a supposedly 50% Baltic German + 50% Latvian got:
89% Eastern European + 11% Finnish & Siberian (DNA Land - 100% North Slavic)
And here is how one Latvian user tried to explain that result:
I'm starting to think some Baltic German families actually ended up with lots of Latvian genes mixed in whether from way back when it was probably most Latvian women around and not many German, or more recently. Some could even be early free Latvians who ended up being considered Germans and the actual heritage forgotten (or hidden for better job opportunities)
And two more people, only DNA Land results this time:
Ethnic Belarusian:
96,0% N.Slavic + 3,9% NW.Euro
Ethnic Latvian:
92,0% North Slavic + 2,1% Finnish + 5,2% NW.Euro + 1,2% Ambig.
"North Slavic" from DNA Land peaks in Belarusians, Lithuanians, Latvians and some Russians.