In answer to your question, YES 50% pen is bad penetration for a double deck game. If I was forced to play that game because I had traveled a great distance and there was nothing better, I would only play heads up or if absolutely forced to, 1 other player. Any more players than that and you are only going to see 5 rounds and probably only 1 round with a reasonable chance at a good count, which is what you are looking for.
HOWEVER, the game in the video is at El Cortez and El Cortez is a little bit dealer dependent, but pretty reliably cut between 60 and 67%. Where you looked at the 9:39 mark, where the dealer places the cut cards looks to be about 60% to me. It is definitely more than 50%. But a better read, is just before the dealer shuffles, when he/she takes the remaining cards out of the shoe and puts them into the discard rack. If you slow the video down (pausing it) it looks like about 1/3 of the two decks, remained. If you take into account a couple cards played after the cut card came out, I would place that at about 65%. We are looking at an angle, so might be distorted slightly, but from the two chances we get, at the end of the shoe and when the dealer places the cut card after the shuffle, I would call it 60%, or slightly better.
Take another look and slow it down at these two spots and see what you think? The penetration estimation is an important skill that may not get enough discussion, because just small differences, can make a huge difference in the profitability of the game, especially at single and double deck.
That is about what it looked like when the dealer took the remaining cards from the shoe and placed them in the discard. I said about 2/3 played. But without looking again, when the dealer did the placement for the new shoe, it looked less, more like the 60% that is pretty common at EC. But we were partially blocked and it might have been a funny angle. Definitely more than 50% though.