Quite the opposite, which is my
point. The Species 8472 beat the Borg hands down without
using their so-powerful-that-adaptation-becomes-meaningless supergun, so that's a further failure to find an example of that strategy ever working.
No it isn't. It's a plot device that gives the Borg a highly convenient invincibility screen. This immediately comes around to bite you in the ass since you now have to have your characters find an equally convenient "Shoot here to kill us all" plot device to exploit.
And this is less exciting than "shoot at them until their ability to regenerate gets overwhelmed", how?
An adversary that simply takes more shots to kill than yer average Klingon sounds just about as boring as adversaries can get...
The second drone didn't "adapt" to anything; the Borg simply sent one with a shield generator as well as armor.
And this is not adapting for what reason?