I already said this before, but i really think that the chances of Borussia Dortmund to become Bundesliga champions this year were extremely high and i don't think that they will get such a big chance again in the next 5 years or so. As you already said, Bayern Munich is by far the strongest team of the Bundesliga and if they are able to at least reach like 85% of their maximum performance level, then they will win the Bundesliga no matter what the other clubs are doing. This year this was not the case and still Dortmund was not able to profit from that. Now Bayern should be alarmed again and take the next season more serious.
It is really difficult to predict the next five years already now. But I can agree with you on the point that there is a much harder season waiting for Dortmund next time. The reason why I think like this is that Dortmund might not get this much lucky about maintaining their title chance until the final moments of the season.
Because Bayern Munich were so much inconsistent this season which helped Dortmund stay right behind them. Even this situation couldn't help Dortmund win the title after a ten-season break. From now on I will be expecting to see a stronger Bayern Munich so Dortmund's job will be harder as a result. Tuchel didn't have much time to implement his plans as he was brought quite late in the season.
But as of the beginning of next season I'm expecting to watch a much better team. They would start with signing a top striker this summer of course to solve the most of their issues.