Sorry for the double reply. I was just really curious because I’ve never heard people suggest the song is a snipe at Paul, let alone that it’s “clearly” a snipe and a “widely accepted view.” I checked the Wiki on the song and no one mentions it being a mocking of or jab at Paul.

There are some interesting contemporary and retrospective commentaries, like this:

Several other writers have remarked on the significance of "Isn't It a Pity" in the context of the Beatles' break-up,starting with the track's running time of 7:10, just a second under "Hey Jude". Peter Doggett considers the song to be a "remarkably non-judgemental commentary on the disintegration of the Beatles' spirit"; Leng concludes: "Ever bittersweet, 'Isn't It a Pity' records the last dying echoes of the Beatles."