The SNP have won a lot of seats through the voting system because the other parties split the non-independence vote. The SNP have never had a majority of votes, even with an overwhelming majority of parliamentary seats.
It has been quite a long time since a Westminster party has won with a vote share of over 50%, and the SNP vote share at Holyrood is higher than those of parties that win Westminster elections. The Westminster electoral system (nb to non-Brits: all the UK constituent bodies run different voting systems for no good reason) delivers majorities at the cost of legitimacy.