To assist in any further misconceptions, all you need is the wheel to be offset a bit and have the pipe be sealed around it, so the steam turns the padfle on only one side due to momentum pushing it foward instead of sideways(mostly).
Example:
_________________________
Ι
__________ --o-- ______
\ Ι /
\ ___/
It would be more bunched up than that, but it's how it works. Sort of like putting only one part of the wheel of a waterwheel instead of the whole thing.
The upper and lefthand blades on the wheel would both see pretty much the same fluid pressure from the steam. That's the problem. And if the wheel did turn clockwise a little bit, the steam would just leak through the bottom to the bottom-most wheel and exert similar pressure on that as well, in addition to steam escaping through empty space near the top (doing no useful work).
This is ignoring the problem of manufacturing concerns. You need to be able to produce extremely precise, tight-fitting parts that can withstand high temperature and pressure (and in a moist environment).
To put it bluntly, yes it would work.
First of all, he's right, all the parts are here already and we just need the physics.
It would, obviously, look different from his little ASCII image, but that's pretty damn close to the horizontal waterwheels the Romans had. Do you know the difference between a waterwheel and a steam turbine? Not much. A case over the whole damn thing and it being made of materials that don't corrode easily. Or, you can use steel and just have to replace it periodically.
Do you think that modern hydroturbines are more precisely machined then waterwheels from the middle ages? Of course they are. If you make anything more precise you make it more efficient. An imprecise machine would still work, however.
Steam is a gas, sure, but it's an unusual gas. Air you can compress easily, this means if you tried to blow air through a turbine the smallest of flaws would cause a huge drop in power. Water, being a liquid, will barely be able to exploit that flaw to avoid having to do work on the turbine (see: push it). Steam is a gas, but is extremely difficult to compress, behaving closer to water than air. You will loose a good deal of energy from any flaws, but it would still work.
Also, the pressure is more dependent on being able to force more through a smaller area than anything else. Have a large boiler and a small outlet pipe and you get a lot of pressure.
You can test this in-game even, if you know how, but clearly fluid dynamics are way over your head.
As for the turbine design, lets put this to rest, shal we: This is based off real-world designs, so yes, it would work.
Z-1
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXX
XXXXXX/ \XXXXXX
XXXXX( O )XXXXX
XXXXXX\ /XXXXXX
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXX
Z+0
XXXXX_____XXXXX
XXXX/ I ===+= (steam pipe in)
XXX/ \ I / \XXX
XXI----O----IXX
XXX\ / I \ /XXX
XXXX\ I /XXXX
XXXXXXXXXXXXXXX
Z+1
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXX
XXXXXXXOXXXXXXX
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXX
In case you don't get it, the outlet for the steam is actually to the side, on the opposite side the axle enters. Bonus points if you make the vanes cup shaped. More bonus points if you slope the ends to point at the direction of flow.
AND I'll say it again, for good measure: You don't need precision parts, it's just more efficient if you do have them.