Yep, I thought Leverkusen use their Academy players, but when I check their lineup in that match, most of them are senior players
https://www.besoccer.com/match/flamengo-u20-juvenil/bayer-leverkusen/202612247/lineupsI think there's no excuse, even though Leverkusen lost Tah, Frimpong and Wirtz, but the current players should able to beat mediocre team. Unfortunately they lost with big margin, this show if Ten Hag was the problem.
In ETH's defense, he downplayed the result. He said he would be worried if it was a competitive match, but since it's a friendly, he's not going to lose his sleep over it. For the sake of his job, I hope he's right. I know it's friendly, and the result may not really matter, but it would be too bad if he loses the next match in similar fashion. Whether he admits it or not, it's not going to look good on him.