Preseason results shouldn't be used as a benchmark for a team's strength, as all teams still have time to make changes before the next season resumes as usual. So, we should all just enjoy the preseason matches as casual entertainment, as every coach will undoubtedly provide the best guidance for their players when they see their preseason results are so poor. And even teams that win in preseason will still make changes for the better, as they have no guarantee of success in their respective domestic leagues next season.
It's crazy to use preseason results to judge a team knowing how less important they can be, it is mostly an extention of training to boost preparedness for the new season ahead, so such results cannot be used to judge a team. I agree the preseason games should be seen as just entertainment and let us use it to see the newly bought players on their first appearance in their new teams aswell.
It can't be a benchmark indeed, but at least we can measure the strength of a team like Leverkusen at this time, whose embarrassing defeat in the pre-season match made many people doubt the Leverkusen team under Ten Hag's coaching and assume that they will not be better in the future, I think it is natural to use this as a benchmark or speculation about what will happen in the future.