Newton's third law states that for every action there is an equal and opposite reaction.
Ronaldo shirt pull is probably a PK, but the moment he throws himself to the ground, I'm thinking, Na....................
The second incident, the defender is pulling out of the challenge, the contact is a 'tap', the reaction is nowhere near equal and opposite. Not all contact in football is a foul, especially when action and reaction are significantly disproportionate
The reason the FA is promoting a high bar for upper body challenges, is because we can't trust the reaction. Both of these reactions should not be rewarded with a Penalty Kick, otherwise all we're doing is letting the players win with their gamesmanship (AKA cheating). We as Officials will never wrestle back control of the game (in general) by rewarding the existing cultures in the game