First: Swain with the new chalice (the old wasnt a viable pick till it got the option to upgrade it) + blue buff makes him remain on lane without calling back unless he needs items.
Second: All the ranges (and the one buffed to 625) got buffed, which means he will trade hits with its alredy high DOT skills before he gets hit, for instance against vlad poke (Vlad who is a very common pick, and swain who is a counter to him).
Third: The new skill AA is way, WAY more fluid than the normal AA, you can last hit way more better with it.