What's unethical is what I said about loading up an almost 20 year old game and making something more accurate, you're suppose to go forward with game development, not backwards, you might be completely fine with 2 seperate games but people like re-creating real life parks/zoo's, including Frontier when they've brought things like Steel Vengence into the game, and the other one (I forget the name)
I don't want to force it, it may not be possible at this point in time, as I said previously, both games are this gens version of RCT1 and Zoo Tycoon, so they may need to go through different iterations before they can be merged in the future, I think its a little silly however to say its a bad idea (going back to people wanting re-create things, and Frontier making RCT3 which had zoo's and the whole moving forward thing) People wanted Zoo's as DLC for Planet Coaster since before the game was released.
If anything, Planet Coaster is a spiritual successor to RCT3 (see above) at the end of the day, is it going to bother you that much or hurt you in anyway? or is it going to be more things for you to play with / try out / keep people happy?