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New research shows a pattern of exoplanet sizes and spacing around other stars unlike what we see in our own system
https://blogs.scientificamerican.com/observations/our-solar-system-is-even-stranger-than-we-thought/
I think this boils down to us having incomplete data. We can detect only a subset of all exoplanets. Until we can collect data on entire exoplanetary systems (their sizes and their orbits), this sort of analysis is doomed to be extremely speculative and unreliable.
Agreed. In our own system, the four inner planets are quite similar to each other in size and composition. Maybe all we've found so far are the inner planets of these other planetary systems?
Let's say someone on another planet were using these same techniques to study our planetary system. To confirm the existence of a planet, they have to see it pass by the sun twice. That means it would take them 2-4 years of study to discover the 4 inner planets, and at that point it would be tempting to say case closed; this planetary system has 4 planets, all of roughly the same size and composition! But if they keep the telescope locked on our sun for another 10-20 years they'll discover a fifth planet; Jupiter, significantly larger than the four previously known, with an entirely different composition. It would take them 30-60 years to discover Saturn using this technique. 84 years minimum for Saturn. Who knows if their civilisation will even survive the at least 164 years of study it would take them to confirm Neptune?