Alec Guinness was 62 yrs old when he shot Star Wars. Sir Alec was an accomplished swordsman, but his style of swordsmanship was fencing in the style of Errol Flynn’s pirate movies, or the older Robin Hood films. David Prowse was a complete novice and could only really thrust in two directions, or perform a couple of blocks.
But the biggest technical problem that they had no solution for was that the swords were made of a light reflective surface as they were 100% practical and not digital effects. And they kept breaking if the blows were too hard.
The combination of a lack of sword skills, Sir Alec’s age and the ropey quality of the sabres led the fight to be a clumsy and slow affair especially when compared to even the following sequel’s far superior fight between Skywalker and Vader on Bespin.
Yet when this hit theatres it was the first ever lightsaber duel that had appeared on screens, and people went NUTS. It is only in hindsight that we can see the flaws.