With the part about RCT3, yes in my opinion that's not really a realistic expectation considering this game was built from the ground up and is not intended as a sequel to RCT3, nor as a rival to the RCT series (saying that from speaking with Jonny Watts btw). I think it's perfectly reasonable to expect things to be added in due course though, but as coolraver said, it's not that simple to just add something new when it's requested, especially in this time period when most of the development time will be spent on bug fixes and performance upgrades.
Regardless of what Frontier's intent was, people who played the earlier RCT games expect this to be RCT4, and they want it to have most, if not all, of the good features of RCT3. To expect otherwise is, in my opinion, very naive. You can tell me a dog is a cat in a different form, but I know it's a dog. If Frontier was making their first roller coaster game, then they could reasonably expect to call this a stand-alone game but they were the developers of RCT3 and the expansions and I'd be willing to bet nobody who played the earlier games actually treats this like it is a completely different game. I know I don't. To me it is Roller Coaster Tycoon 4 no matter what they had to call it for legal purposes. And it will continue to be compared to the earlier version. Frontier may think they are reinventing the wheel, but they're not.
Except for the graphics and some of the building features, I don't see a whole lot of improvement that was worth waiting 10 years for. The pathing system is often unwieldy, the choice of which items have the 3D manipulator available seems arbitrary. Standard scenery items like fencing, lighting, seats and tables are minimal if they exist at all. Terrain painting in a number of areas is all but useless. The selection of decorative foliage, aside from trees is anemic to say the least. No flowerbeds, no actual flowers at all. Blueprints aren't saved as one building so you have to rubber band select the whole thing to move or manipulate it after placing, which can be problematic if it's near another structure. There are virtually no interior decorating features, including flooring or wall coverings, or the ability for anyone else to create any, so far.
If they were using an established engine for this game, like Unity, for example, I'd say they did the best they could within the engine's limitations. But they built the engine! These aren't limitations, they are design flaws brought about because they had to rush the game to get to the Christmas season for release and because they had to compete with RCT World.
Frankly, if I wanted pathing limitations, buildings saved in pieces, or collision detection for scenery on rides, and poor custom content management, I'd be better off playing RCT3. Because at least the park management isn't as much of a royal micromanaging pain in the neck. And with two expansions, path covers and years of custom content, I can still build almost the park of my dreams. In many ways, it's a far better game than this thing is right now.
And Frontier better start listening to the volume of complaints they get, because most of the people I know who played from alpha to release, are jumping ship in frustration. I'm one of them, although I didn't play the alphas, but I closely followed the forums and the development of the game. Personally, I just got tired of fighting the path snake.