some things to note:
Aliens can't see through 4 tiles of smoke. which is the same for xcom. Smoke does work both ways, but xcom can choose where and when to pop smoke, so thats advantage xcom.
I don't have much experience with smoke, so you are probably right here.
Come to think of it, disposable soldier with smoke grenades seem to be somewhat worse alternative due to need to prime these, but then again, it can be done in advance and throwing usually gets better accuracy (than 0% for vehicle launcher) with same TU costs.
Just because it takes the space of one unit and behaves like a unit (ie - can move/spot/die) it's still not really comparable to a unit. A tank is a tank... it's designed to take hits and provide fire support... this is not tank. think of it more as a deployable tool.
I should've probably stated clearly that all comparison points above are to using soldiers in place of a vehicle, not tank scouts, which are much worse than soldiers at that, at least until hovertanks.
that said, it is kinda flimsy... a good shot with just about anything can take it out. I suppose the problem with that is aliens are only armed with plasma weapons... so you need good-decent armour just to survive a hit anyway, so increasing the drones armor wouldn't stop it being one-shotted unless it got a good buff. However... it's not a tank, high armor doesn't really make sense. It's tricky...
One potential I see for such tool being useful is advanced sensors - always-on night vision (like aliens have, presumably through biotech and/or implants) might be nice (<insert comparison with flare-packed rookies here>).
Maybe an even better vision? Built-in motion scanner?
Other sensory equipment that don't fit on humans?
Not sure how much of that can be done from the mod though.
sacrificial rookie tactics... I don't really use 'sacrificial' cannon fodder, so for me this helps save lives. and in terms of lives saved... if you use the drone cleverly, you can avoid meat grinder situations where 3-4 rookies run blindly into danger and get killed. these lives saved add up too. Ideally I'd like the drone to be stealthy, I tried to implement that by giving it high reactions (to avoid incoming reaction fire) but a side effect of that is the drone wastes its smoke shooting at aliens as reaction fire too ._. It's also a smaller target, so aliens will have a harder time hitting it. these little things help it's survivability, atleast thats the theory.
I didn't realize there was a height difference, that should be another "+" point, though not sure if it affects the actual aim either.
After casual glance at Projectile::calculateTrajectory, I think it should, as what seem to be calculated there is not just whether shot will be hit or miss, but "target voxel" (which I assume is smaller than 3d tile, given that projectiles hit fences, window frames and such) - the point in 3d space which projectile will actually fly to.
"sacrificial" can be replaced by "first out of the door" usually - someone/thing has to go and spot aliens at the end of the day, and that one/thing has good chance to die, so no point sending best shooters there - they are much more useful at shooting spotted stuff and will become even better at it (as they get kills).
-- After the very early game stage, rookies have better armor and still cost way less.
- Saving rookies will get "trained" to better class, so saving them is useful? DONT YOU LOVE YOUR SOLDIERS! 
Putting extra value on human life in this case seem to be at odds with game mechanics, where you get "TANKS DESTROYED (1): -50" vs "X-COM OPERATIVES KILLED (1): -20" - clearly lives of even most experienced and decorated humans aren't worth even half of fried silicone and gears they put in that tank, further confirmed by the actual price tag of soldiers vs tanks
Guess overpopulation, mass indoctrination and lack of raw materials for good tech in the world of x-com might explain how such thing came to be.
Another "+" for fair comparison would be that you don't pay monthly wage to the tanks, like you do for soldiers - at least cruel world of x-com doesn't have them die as slaves or battle thralls.
as for delivery times... it's standard delivery time for a tank if I recall, I could up it to standard delivery for equipment I guess.
Don't think it's that huge of a deal, but might be one more advantage over meatbags.
