You are right and it is very clear that Kaiserslautern performance in Bundesliga 2 and the DFB Cup is very different, here Kaiserslautern has really succeeded in beating many teams that are far above them to be able to enter the final like now.
For their Bundesliga 2 position, they are really uncomfortable because there is pressure to be able to complete it to have much better position with the remaining matches.
This is clearly not an easy thing for Kaiserslautern but on the other hand they also have to prepare their performance for the final match, even though it is impossible for Kaiserslautern to beat Leverkusen but at least they are strong team here.
Who knows what will happen later for Kaiserslautern in Bundesliga 2 but the important preparation is this final match and they must be able to focus, at least to be able to provide tough resistance to Leverkusen.
Trust me, the German cup final is not in their minds at the moment, at least the coach will tell them not not have it on their mind.
These upcoming 4 games in the 2nd Bundesliga are WAY more important than this final.
Sure, the cup is prestigious, and also comes with a cash prize, but being relegated to the 3rd league would cost Kaiserslautern MUCH more money than what they will get for a cup win. Once you go down it's hard to get back up immediately cause many player's contract isn't for the 3rd league. So there will be a rebuilt with cheaper players because of less TV earnings, less advertisement money and so on.
And let's be fair, their chances of winning are so small, it would be wise to focus 100% on the league games before having their mind anywhere else. Doesn't mean they can't win, 1% chance is still a chance.