You are certainly not wrong but do bear in mind a few things. First, the engine was modified between planco and planzo and it can be modified further for a sequel or even revamped.@ChicagoZohan Ive seen best in slot play the alpha to PK awhile back and it does look good. You mentioned resizing objects and stuff which are great features as well. I got a feeling now since PZ has been out for a couple months competitors will look at what PZ has to offer and what they could offer to compete. Not necessarily referring to PK but any serious zoo style sim that would come out would more than likely add the things PZ doesn’t have or couldn’t offer. As for PC 2 I think it would obviously be much improved but if things like the ability to create functional water parks and other shortcomings the first games couldn’t offer it would still be disappointing in that regard. I enjoy both games but like PZ for example people want underwater swimming animations and animals and zt2 which is much older offers both of these you have to start questioning the cobra engine at that point.
And remember that when Zoo Tycoon 2 came out there were only two depths of water and underwater terrain couldn't be modified. It was Marine Mania that added those features.
On the other hand marine mania was an expansion pack and so far the Planet series has only had smaller DLCs. Is it possible that Planet Zoo will see some true expansion packs like an aviary or aquatic animals? Maybe....