It actually showed how much more powerful the Borg are than the Federation. Picard's orders were to investigate and keep the Borg busy while a fleet was being prepared to properly fight the Borg. Picard went in knowing it could well be a suicide mission or at best, a game of hide and seek, to keep the Borg occupied.
Yes, Picard knew from the start that the borg's military technology is far better than the federation's and that the borg massively outgun his ship.
He also knew that drones can easily teleport through federation shields and are, individually, more than a match for his men.
And he found out that the borg wanted him - personally.
Yet - there were no additional security personnel (or measures that fulfill the minimal standard of springing into action at his capture - we're not even talking about being effective) on the bridge or any other part of the ship; no other measures to prevent his capture (yes, up to and including suicide pills).
As said - Picard was either incompetent or ridiculously naive; most definitely culpable.
Interesting idea about suicide pills, but that does highlight an important aspect of TBOBW. The Borg should not have been allowed to get their hands on Picard, though I wonder if the Borg would have just picked someone else fairly high up the ladder? In any event, Picard's capture compromised the security of the entire Federation. I'm sure the Vulcans were significantly unimpressed by the lack of "the needs of the many outweigh the needs of the one" actions there.
The borg's assimilation gives it a huge advantage over anyone that doesn't have equivalent means of extracting information from captured opponents.
One captured commander and the borg knows everything, ranging from essential strategic and technological data to quirks of field captains.
Even if one can match the borg ship-for-ship and gun-for-gun (and, as we know, the federation is not even close to being able to do that), this tremendous intelligence advantage should give the borg victory every time.
This means that any and all measures to nullify this advantage of the borg should be routinely taken - up to and including suicide pills for all command level personnel.
And if said personnel is not willing to give their lives in order to safeguard the federation (preferring instead assimilation), then they are not fit to be on a starfleet ship's command deck.
Indeed, starfleet personnel is expected to give their lives for far less - in order to save a single ship, or a single colony against the attacking romulans/whatever.