The problem with most submission holds is that, if applied correctly, they do actually hurt (probably the most painful being the figure 4 leg lock, in my opinion - the joys of two brothers growing up wrestling fans... Don't try this at home, kids!) and there is a fine line between making them look convincing whilst not hurting the opponent, and actually applying them correctly.
I guess this is why only very few people in WWE have taken Chris Jericho's Lion Tamer (Daniel Bryan, Kofi Kingston, Adrian Neville, CM Punk are four that spring to mind but not many others) and he replaced it with the much less painful looking Walls of Jericho. In line with comments above, note the four names listed are all smaller wrestlers, where Stone Cold, Triple H, the Rock etc are larger body types, presumably taking a Lion Tamer would have been too risky for them?
Bret Hart managed to sell the Sharpshooter as a convincing finisher (as did his opponents) without having to apply too much pressure, in the same vein as Rusev with his camel clutch. Despite having shown us that he COULD make it look genuinely excruciating (his SS on Mr Perfect at Summerslam '91 is one of the most painful looking moves I've seen in WWE - remember that, despite what wrestling tries to tell us, the Sharpshooter does more damage to the lower back than the legs), Hart successfully used a less-pressure version for almost the entire remainder of his career without complaint.
Obviously there are some moves that just look terrible - Cena's STF most of the time (only because, logically, the opponent could easily slide Cena's arms over their head due to the obvious lack of pressure), and I'll never understand why, logically, a person applying an ankle lock doesn't sit or kneel like Ken Shamrock used to do, but generally speaking, most submission moves are fine as they are.
That said, all this talk about Lana and Summer Rae's flexibility - damn I need to check out Raw!