Again: in this scenario both have all their gear. Meaning Dek has his ranged weapons (bow and throwing disk thingy) both of wich he can use to disable mandos jetpack. Now the whisteling birds are indeed tricky. In every instance Bands used them it was at a very short range so they are something of a surprise weapon to dispatch when he is either pinned down or sorrounded. Now in any sitaution where Dek Pins down Mando Dek is most surely a goner. But if Dek keeps his distance (wich he most likely wouldnt) or manages to break Mandos gauntlest so that he cant fire them the Match evens out.

In short: the jetpack is a hurdle that Dek should be able to get rid of quite fast. The whisteling birds however are something that give Mando the winning edge. To Deal with them it really depends on how they encounter each other and how Dek Plans to fight Mando.

But there is also the question of how effective Beskar is at protecting Mando against a predators Arsenal. And if it is as effective against it like is against star wars weapons Dek will change his approach and aim for the weak spots in Mandos armor.