It really depends on the type of shield - as @Neonchameleon pointed out, viking shield usage was different, and bucklers certainly were used differently too. However, the type of heavy shield protecting mostly the torso used in this film was fairly similar to the ones we used, and heavier too - 13 to 18 pounds if a quick googling is accurate.
Yes, your typical Aspis (
Aspis - Wikipedia) was about 16 lbs. or 7 kg., but depending on the size a range of 13-18 seems reasonable.
Although definitely heavy, as you should know the weight was carried mostly on the shoulder through the elbow, keeping it close. Now, the types of attacks Achilles (primarily) is doing with his shield would be fairly easy for someone with his apparent strength. Judging from the designs in the video, I would assume Hector's was the heavier of the two shields, and he didn't use it as offensively, often barely able to get it into position to deflect Achilles's thrusts.
Honestly, as for the shield use in the clip, neither seems to be using the shield focused on defense. We see a lot of "dodging" etc. but that makes for a more exciting scene so I get that here...
But why wait until Achilles' spear is free?
IIRC because he was using not just the shield but his whole body (pretty much) to force Achilles's spear down? I doubt he was in position at that moment to counter-attack.
See, I don't think it does because Achilles is not human, he's almost a demi god. I guess it depends if you think that D&D heroes should be heroes or superheroes?
Yes, Achilles is a demi-god for the most part. At the level he would represent, many players do see PCs in D&D as superheroes. Even the DMG calls them superheroes in tier 4, which I would certainly place Achilles in. Hector, however, would be solidly in Tier 3 IMO.
Anyway, thanks again for the discussion. I think the clip is good for what it is, and "more realistic" shield use would be less "exciting" for viewers.