Actually I had offered "(not-so-)old school" isometric graphics , so no Unity etc involves. I think it is easier to achieve than going full 3D, AAAs set bar too high for decent 3D graphics.
- Using 3D with fixed ortographic projection may look easier at first but I think even "manpower" required to make assets low-poly yet hq is much more work, you go high poly other way. (especially if you are not giant Swiss army knife)
Not in the design field, so I'm not going to chime in on that stuff, but as an artist I have to say that's actually kind of a big misconception.
A lot of people have said things along the lines of "Well, it'll be easier on you if it's 2D, right?", and at least in the context of me I can understand where the sentiment comes from. Most of what people see from me is 2D, so they're basing it off that. But as a generalized statement, 2D is not necessarily easier to achieve than 3D.
"Full 3D" means you don't have to draw/paint/pixel the same sprite from multiple angles if it doesn't work to just flip it, and if you made them in a modular way you can just scale up and down and move pieces to easily create new buildings that follow the same style/universal rules. They can even use the same texture sets!
Now, of course, you can make modular 2D assets, too, but hand drawing is a little more time-intensive. I should think having to draw different angles of near-everything, combined with the fact that scaling modular pieces can be near infuriating depending on the art style.
Additionally, at the scale of your generic "city simulation/tycoon" game, it would hide most all of the actually difficult 3D work, like hiding slightly iffy seams and the place where objects intersect (as you'll never really be close enough, even zoomed in).
The bar for 2D graphics is no lower than 3D, to be honest, and having worked with both, for something like this I'd pick 3D over 2D to work with any day. I also believe that a good 3D artist (eg: the one you should be hiring) wouldn't take anymore time to create a usable asset than a 2D artist.
Just my 2 cents.