That's not sucking at blocking thats YouTube intentionally adding a delay to make it seem like their experience is degraded when it isn't. If you turn the slider up to full it only happens very rarely.
I'm sure this will all change eventually though and YouTube has a loophole planned so ad blocking on manifest 2.0 is impossible.
I'm not really sure of the actual mechanism, but on Firefox with a fully updated block list the delay doesn't seem to happen for me. Whereas I could never quite get rid of it on Chrome. This was a while ago, though, when they first introduced it.
I use uBlock Origin with Firefox on Linux, and it seems like that delay happens maybe on 30% of the YouTube videos for me, with no rhyme or reason to which ones. And reloading the same video multiple times show consistent behavior if it loads fast/slow, not sure what's going on.
I'm sure this will all change eventually though and YouTube has a loophole planned so ad blocking on manifest 2.0 is impossible.