Doing something similar to Rollercoaster Tycoon, isn't that a bit too much asked from Construct 2? Perhaps like Prison Architect - I never played it but saw that is was top-down - it could be done nicely that way. Perhaps some 2D (not isometric) like shadows or at least some illusion of an extra dimension besides top down would make it only much more nicer.
Have you done some research on such theme park tycoon games already existing on the web? Mobile is definitely getting more and more popular, and tycoon games seem to have a never ending demand. But yeah, RCT on mobile is quite professionally done, lol, so you will be in direct competition.
Why not go for the desktop audience, you could sell many licenses (if your game is well done) and I don't think the big sharks are going after that. The way I grasp it, is that the big kahunas go for the big bucks, obviously. They have everything to make a game look and play that great.
I don't know how much time you have on your hands, how fast you work, and if you can do everything on your own, but if you got what it takes as an indie developer you can afford to make errors. Why not go through with it and gain some experience? We don't know much about your plan, do you want to make thousands or would a some pocket money and experience be satisfactory?
In any case, I am kinda excited to see what you have so far. I believe I saw a 'demo' of your theme park idea once, I thought it was kinda interesting and am curious as to how you developed it so far.
Anyway, from my online marketing experience, it's better to go and take your piece of the pie / piggy backing on a trend rather than doing something that has never been done before. If you do everything right, make it interesting, sound and look good, you shouldn't have to worry about the concept itself.
P.S. I know little about marketing your game on Steam but I always felt it's swarmed and even greenlit games get little exposure simply because people generally go to Steam for high quality or AAA, or at least AA titles. I got the idea sites like Kongregate are much better suitable for games made in Construct 2.