Leverkusen was not going to stay unbeaten again, this is simple football logic I expect the fans to have really understood before have the unrealistic expectations of the team, since the erra of morden football, I doubt if there have been a time any team has been able to maintain an unbeaten record at least twice in a row, so expecting Leverkusen to have done that is really crazy, they should be applauded for their last season performance already and allow them do that which they can do in this new season and not necessarily trying to keep hopes high for them and later feel disappointed. The most likely realistic achievement they can really get at this point is winning the bundesliga title this season but unbeaten again is typically far from it.
You are right dear it is not realistic to think Leverkusen can go unbeaten again. In modern football it is very hard for teams to win every game even for just one season. Fans should be proud of what team did last season and enjoy their successes. They should not expect too much and then get disappointed. Winning league title is more achievable goal and Leverkusen should aim for that.
It is important to be realistic and not put too much pressure on team. Leverkusen has already shown they are strong team and fans should enjoy watching them play without expecting them to win every game.