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.
It's normal for friendly matches not to be taken seriously. Because the manager makes changes based on his own preferences, deciding which positions certain players should play in. Furthermore, conceding five goals despite being a youth team is a major problem. This needs to be said, but I think ETH is making a mistake by ignoring this. They should definitely emphasize the importance of these matches to their players. You should definitely criticize a defensive line that concedes five goals against a youth team, and you should support that section.