Planco got one year of free updates before there even was a paid DLC. Planco also got a big anniversary update and - believing the Planco people I interact with a lot - there were more hints, a constant buzzing and more insight to the process than there ever was with PZ. So I don't feel like we are still in a situation were we can compare these two. Things have changed and I don't see it changed for the better.
I see your point about that but would only say that the most of the free updates in the first year were mostly features that were clearly planned in to the base game (security guards being the obvious one). The really big first year update was in summer 2017. Plus Planco got a long alpha play testing period which meant there were far fewer bugs on release although you could look at it as menaing players had longer without a lot of key features (first couple of alpha builds didn't even have coasters). Now a legitimate criticism I can understand is that PZ felt rushed and should have had a longer beta and you are right that paid DLC came out much faster for PZ which suggests they have tried to get new money in a shorter development timeframe. I also suspect there probably is a smaller team for PZ and I also agree that the 'buzz' has been less. I do think that's partly inevitable though - Frontier has got bigger and is now the lead developer of a much larger number of games whereas Planco was basically their only big launch for about 2 years. I suspect the Elite Dangerous lot were resentful that the Planco community got so much attention during that time (and they had a roadmap that got delayed as well!).
I guess I just feel like, and this might be unfair, that some of the negativity is being generated by the community itself. Personally I think PZ was a more complete game than Planco was at launch (despite all the bugs) and every time they do introduce something like the coat variations people seem to be disappointed. I don't know if we have higher expectations as a community or it's something about zoos, biodiversity and animal behaviour just being harder to do because people want to see it simulate the real world when that isn't possible. Maybe everyone is just a bit down because of the global pandemic or maybe it my own grumpiness bleeding over from my day job. I work with climate modellers sometimes who are constantly trying to mimic incredibly complex systems in the real world but who are constantly under pressure because it's not accurate enough.
I guess I feel some of the things you are talking about - parental care etc. are probably not worth the processing power or development time versus guided tours or diving because I'm not sure it will ever be good enough. I do feel they got the herding behaviour better and babies now follow their parent a lot more. So it starts to come down to personal preference about priorities and that's where the whole challenge to me is harder than planco - every flat ride in planco behaves the same and it does the same animations on repeat and it doesn't have to have any pathfinding so it's just easier.
Personally I'd like them to bring in a trait system to the animals so that some are more fearful or like swimming more etc. like they did with guests in Planco but I know that they may have to balance it against any performance hit adding more complexity to the behaviour system would bring. I just don't want people to assume it's 'laziness' or a lack of interest in the game that is driving Frontier's decisions. It might be that but it might be other things as well - them putting in more developer time or more 'effort' might not change the outcome at all