I asked the same question to the instructor of my USCG boating safety
class. He has a captain's licence. He said "NO WAY" was a pontoon boat
safe on open waters. In fact, here in Maryland we had a pontoon water
taxi flip over in (protected) Baltimore harbor due to strong wind.

That boat flipped for more reasons that just being a pontoon boat. The
captain took it out in conditions that other boats refused. And it's
enclosed design practically made it a tomb, as was borne out by the poor
souls unlucky enough to get trapped when it capsized.