At 100 meters, the PTRD can penetrate 40 mm of armor (with a bit of good wishes) so the flank of Panthers and Panzer IV are definitely vulnerable. Books I’ve read disagree on whether the armored side-skirts were for defense against Bazooka rockets or AT rifle plinking.
Any author claiming that side-skirts were intended to defend against Bazookas has not done their homework. There is evidence aplenty that they are for defence against anti-tank rifles.
The vertical component of a Panther’s side armour was only 40mm, but the only bit vulnerable to the anti-tank rifle was that between the top of the roadwheels and the bottom of the sloped superstructure. Hence the miniskirts that Panthers wore when compared with the Panzer IV’s full ballgown.
Less enthusiasm, please. This is Britain.