Indeed it was extreme example and did wonder about using it. I agree they're important and there is pressure. Its definitely a skill for sure, the best ones over time are usually mentally strong with ice running through their veins. particularly if its a game defining penalty - then add in being away from home in a hostile atmosphere.
Reality is though, if you were to offer a manager a guaranteed penalty every game or 2 half chances, I'm certain they'd take the single guaranteed penalty every time. The stats are that 3 quarters of penalties are scored. Over the course of the season thats roughly 35 goals.
A squad of professional footballers is always going to have a couple of above average penalty takers, as it just needs someone to be cool and be able to strike a ball cleanly. The squad is pretty much guarenteed to have a number of composed players, they then just need to be able to strike a ball cleanly - which again, by being prom footballers who've been kicking a ball, practicing most days over 20 years, is a given.
The variables involved are nothing like scoring from open play. I get that some players are better at being instinctive than dealing everything that comes with a set piece. But due to all the possibilities involved with scoring during a game, those players are much more valuable than someone who slots home penalties.
Gloria may say some players find it easier, but a player that consistently finds himself with and converts easy chances when having to deal with top level defenders, different angles, positions is going to be making himself and clubs he plays for an awful lot of money over his career. A player that consistently finds himself with easy chances at the highest level(and converting a high %) is incredibly valuable... it simply doesn;t happen by accident in elite football unless you have something special about you. Generally a player thats getting that many chances is going to be surrounded by top players that create chances, because he's a top player himself. If he wasn't, he wouldn;t be playing in that team!
I'm pretty certain, in fact there are, lower league players/strikers who are deadly with penalties and if they stepped up to the PL just to take pens, they'd continue with that high conversion rate (maybe once adapted to larger crowds), but they'd be out of their depth leading the line and being relied on to score 10-15 goals from open play (even with better players around them) as their finishing, technique, pace, anticipation, positioning, strength, football intelligence - or whatever mix of key attributes, wouldn;t be good enough.
Basically, put most prolific League 2 strikers/penalty takers in a prem team, and he's highly likely to continue his penalty conversion rate, or at least close to it. It's extremely unlikely he'll get anywhere near the same amount of goals from outfield play, as he'd get marked out of the game by top level defenders, despite have better player around him. If that wasn't the case, why would top tier clubs pay 10's of millions for strikers, when they could sign someone from the lower leagues for a fraction of the cost all the time?
I'm not saying its 'easy' as such to score penalties and it does require certain attributes, and of course at a high level a goals a goal, but thats too simplistic and not accurate when you drill into it further.
No one is questioning the players you mentioned as they also scored consistently from open play at the highest level for years. If you started saying x was better than x because he scored more, people may then start looking closer at other stats, such as how many were penalties.
Anyway, too much coffee, sorry for long post!