I can imagine there are many aspects that need to be discussed by and by. I don't think there is ever a valid reason to equate Svensson and Månsson - but I should think that there will be quite a lot of valid name variants for -son names that sound strange to us Swedes but actually occur among emigrants. Well, it's common knowledge that Svensson often became Swanson - I don't count that as strange ;-)
I think the worst source of falsely matching surnames for -son names are with sons of Johan, Jan, Jon, Jonas and the like - looking internationally there are just TONS of valid variants. We'll have to live with that.