Still they managed to capture both Kalmar and Älvsborg fortress, some quite good prices and they had the opportunity to move further north had not England and the Netherlands intervened diplomatically. Altough it would had come with a heavy prices as luck started to turn.
And the Norwegians were actually instructed not to move in on Swedish soil but just keep them out and tie up Swedish resources.
But I'm into the bad monarch idea as since Kristian IV they managed to do little still being in the same position as they had been earlier.
As may have been mentioned they put to much trust on mercenaries instead of developing an own recruitment policy, thus hampering effective training of experienced officers. Another choice to blame the monarchs for?
They did manage to capture those fortresses but it was a major deviation from plan that had envisioned an earlier easier capture and then move on Sweden proper. The offensive died in the tracks with a lot of Swedish help.
One of the main reasons the King relied on mercenarys was the old struggle between king and nobility - the king could tax the merchantmen going through the Oeresound but he couldn't levy troops within the KINGDOM without the consent of the nobility!
Thus the king were able to levy toops in the Duchies and rent his own mercenarys thus circumventing motivating the nobility to take a greater part in his wars and keeping control himself - all leading to autocracy in 1660.
And do remember the British and Netherlands were not interested in wars in the Baltic as it would upset trade in timber, hemp, grain ect. crucial to themselves which really got the right treatment in 1658 when Denmark lost Scania thus couldn't bottle up the Baltic!
You can't blame the monarchs for doing what they did as they percieved themselves of having gotten the right to rule by GOD, as every other monarch did.
They just had to adapt to their environment which meant a hostile nobility bend on attaining power at the expense of the monarch.
They had to make choices due the their situation they didn't as we have the wondrous advantage of hindsight!