Jules I had a 4.13k bub (9lb1oz) & did no masage with no tearing at all. I think when you logically conclude that passing a medium watermelon (for want of a better object) through a hole designed for a lemon some women will inevitably tear & some wont.

This goes to variables like skin elasticity, size of the baby etc. Experienced & patient midwifes can minimise risk by asking you to wait, stop pushing (which can be a big ask at that point) & realigning skin/bubs head etc.

If perenial massage will give you a sense of mental preparedness then go for it, that can only be a benefit but my personal opinion is that, as with all statistics, it is truly a numbers game. Some tear & some dont.