So why does Sweden & Norway have more R1a haplogroup like Poland & less N haplogroup like the Baltic region & Finland?<quoted text>
The keyword here is mesolithic.
Mesolithic European is most preserved in the Baltic region.
For all we don't know, northern Poland might have had the same mesolithic mix than the rest of the Baltic Sea regions.
The connection via Gotland and Saaremaa / Curonia / Prussia is well known and documented. It worked over many millennia. Swedes might not literally be the descendants of estonians, but gotlanders are about 50/50 mix of southern baltic finns and (coastal) swedes.
Much less is known of any neolithic connections between Sweden and Poland.
While I was mixing mesolithic with neolithic, you are mixing neolithic with paleolithic.
Scandinavia has had about the same zones as the Baltics and Finland. Meaning that estonians and balts are more similar to swedish south of the Stockholm latitude, while finns and saamis are more similar to swedes north of Stockholm. The difference in importance comes from the higher population densities in more southerly regions.
And btw, I very much doubt that any substantial population migrated to Sweden from the Tatra and Carpathian mountains.
There is a direct connection between Poland & Sweden by Cordedware culture.
R1a haplogroup, Indo-European languages & Nordic phenotype went from Poland into Sweden in the Cordedware culture.
Sweden was a part of Kurgan culture.
Earliest Kurgan found in Poland 6,000 years ago with other of the earliest Kurgan's found in Ukraine & Russia 6,000 years ago.
A Kurgan is found in Sweden 4,000 years ago about the time of the arrival of the Nordic phenotype & Cordedware culture in Sweden.