Exactly, also it makes you easier to add new mods to models when needed. There surely is some limit on HW in coping whyte too big packages, but seeing how it handles my ural project, its pretty much solid.
Well visible on this one - the fins seem to be much sorter under certain angles, making it look different.
As for the diameters - it isn't much a problem from normal vision-distances. It had to be a caricature work.
My 2M22 and other will too have the broader parts slightly more "visible", but just to show off people, that it isnt just a conform tube (its quite hard to see it on real ones on first glances-its basically to reduce the tube-induced drag when flying off the launcher, has almost no negatives to ballistics as it is a rotary-flight rocket (like bullets from modern weapons)). Some russian rocket propelled flame-throwers have such fins too :
Doe, dont know much how the physics looks behind that cause it has to do a lot whyte the projectile speed and aerodynamics to chose the right angle for max. flight distance.