Those three names that you mentioned did all get shot's at the WWE title but simply didn't win the title but for all the people who said Mr Perfect was never a World champion he was AWA World champion at a time when that was classed as a World title and AWA was a major wrestling company. Curt Hennig beat Nick Bockwinkel for the AWA World title and went on to hold it for around a year and this was at a time when Jerry Lawler, Nick Bockwinkel, Ric Martel, Stan Hansen, Wahoo McDaniel, Scott Hall and The Rockers all on their roster at that time plus many more.
With Davey Boy Smith i think he was simply in the same boat as William Regal, Dynamite Kid, David Taylor, Paul Burchill, Finlay, Drew McIntyre and Wade Barrett in that there has never been a WWE/World champion from the UK and he was never seen as many more than a mid carder but he had shot's at Bret Hart, Shawn Michaels, The Undertaker and also in The Six Pack Challenge in 1999 at winning the WWE title. As much as i liked Davey Boy Smith he just never made me believe that he should or could be WWE champion and was much better as one of those wrestler's who move up from the mid card to work with the bigger star's when they needed putting over or someone to feud with.
The thing with Owen Hart though is that he almost certainly would have gone on to be a WWE/World champion had he not tragically passed away in 1999 because WWE had HUGE plan's for him once the whole Blue Blazer thing had finished and that was said to be planned for a couple of months after the accident. The character that Triple H was given as The Game was meant for Owen Hart and they were going to push him as a serious style top heel and seeing how Owen Hart was around the same age as Shawn Michaels and The Undertaker i have always believed that he would have gone on wrestling until a least 2007 which would have meant he would have a good five years with two main title's in WWE to go after.
When you look at it though with people like Owen Hart, Mr Perfect, Davey Boy Smith and also people like Ted DiBiase, Rowdy Roddy Piper, Scott Hall and Rick Rude to name a few others their main problem was who was around at the same time as the majority of those names had Hulk Hogan, Randy Savage and The Ultimate Warrior around at the same time who between the three of them basically held the WWE title for something like7 or 8 out of a 9 year period because they were the biggest draws and stars. Then later on the rest of them had Bret Hart, Shawn Michaels and The Undertaker all ahead of them because they were the biggest stars and draws for their era but also were the best in ring workers at that time as well but there was only one roster.
In todays WWE though there is only really John Cena, The Undertaker, Triple H, Rey Mysterio, Edge and Randy Orton who are big stars in the wrestling industry with CM Punk a possibility because he is former three time World champion but because there are two seperate rosters now it means that they is in reality maybe three big stars on each roster meaning that people who a decade ago wouldn't even probably win a mid card title are now a WWE/World champion. Mr Perfect and Owen Hart would be multi time WWE/World champions if they were wrestling today when you consider some of the people that have been WWE/World champion since the brand split but unfortunately they were from a different era and missed out because of who was around at their time.