That is not quite the case. Those who gained the throne through conquest were seen as usurpers and there were people who fought to restore the legitimate line back to power. England is a good example. When Henry of Bolingbroke overthrew Richard II and became Henry IV, there was a rebellion that sought to restore Richard to the throne, which is why Henry IV had Richard murdered(which indicates that Richard did not willingly abdicate and him being alive was a threat).It literally does when it come to royalty. The right of conquest superceeds the claim of blood as mentioned earlier. Victory or defeat in war was historically seen as the will of God.
You could become king if you could muster the manpower to beat the crap out of anyone who said otherwise. That's basically how nearly every royal house ever came into being. Even the ones who didn't like Sweden's House of Bernadotte are only there because Napoleon would kick the shit out of anyone who said otherwise about their ancestor taking the throne.
There was the Southhamton plot against Henry V and there was later the Wars of the Roses that caused the overthrow of the House of Lancaster. After Henry VII seized the throne, he had to marry Elizabeth of York to secure his claim to the throne. After the Glorious Revolution, there were the Jacobite uprisings.
These facts showed that many considered thought that claim of legitimacy superseded the right of conquest.