Obviously, there are guitars that are easier to play. With the same model, some guitars are easier to playthan othes, in spite of the fact that the action is about the same, all others factors ( neck thickness, nut width, etc) are the same. Then, it's a mystery. So, the only way is to try the guitar before buying it.
In my opinion (you may strongly disagree with this), string tension doesn't affect playability much. Of course, your hands feel tight with high tenstion. But it doesn't mean switching to low tension can solve the problem of your guitar's playability. Low action doesn't guarantee good playability. I saw some guitars with high action are surprisingly easy to play. I also saw some guitars with low action are surprisingly difficult to play.
The previous posts all mentioned the factors that affect playability. I'm not going to repeat here.
When I think my guitar is hard to play, I do the followings.
1) lower nut height. Most factory guitars have high nut.
2) lower the saddle.
1) and 2) are what all of us usually do: set-up.
3) level the frets: frets affect playability more then we usually believe. Even though there are no high frets, or no buzzings, I sometims do fret work to improve playability. Here, for example, I often modify neck relief, or I sand down treble frets or base frets more to achieve height balance (or tension balance) which improve left hand bar position. Fret leveling and crowning require a lot of experiences, but once you learn them, you ll be happy until you die, saving a lot of money. Especially most old guitars need fret leveling and crowning. So when you buy old guitars, be careful!
4) if 1),2),3) don't work well, throw away your guitar. (I'm not a luthier, so I can't modify neck shape, fretboard shape, neck angle, re-freting etc.)