Serious question, is it also a possible factor that the RNG algorithm in FFXIV is.. at least by reputation, quite bad at generating series of independent results, with both losing streaks and winning streaks too often appearing in clusters over time?

If you are getting a 'no portal' result, you would to be moving through your locations rapidly because you move right on to the next one. Whereas if you do get a portal, it is going to take time to clear, during which a time period in which 'good result numbers' were experiencing a cluster might be over by the time you get to your next map. So if these supposed clustered 'rng result streaks' are real, it would make sense you would be opening more maps during a streak of bad rng numbers than during a streak of good rng numbers, right? And such an effect would bring the experienced rate of success always below the theoretical average rate of success.