Why would you be disappointed about that? Any planet must have a maximum amount of resources they have to sustain a population. Then increasing this with tech or farms on the planet would make sense
While that is obviously true, it would definitely be a 'soft cap' in reality, given that different species would have different impacts on the environment based on their size, living requirements, respiratory systems, etc, and that's before you start factoring in technological solutions.
I'm not entirely sure how the cap will be handled in Stellaris, yet. The impression I got was that each 'province' on a planet can hold one pop, and you can create more space by freeing up 'blocked' provinces. I understand why they did this, and it's not a dealbreaker, but I can't say I'm a fan. At least not yet. I am open to changing my mind once I get a better idea of how it works.
I'm not a huge fan of hard caps on anything, frankly. I like natural fulcrums, where the system tends toward a peak in terms of efficiency and cost. Because this lets the system fall out of balance, or be pushed out of balance by the player to achieve some goal. With consequences. It's tough to imagine that kind of dynamic working with a 1-province/1-pop limitation, but it remains to be seen how things will actually play out. Paradox is pretty clever with systems, so.