Petroleum is a good fuel because it stores well, burns well and simply, and is plentiful, while it is much better than ethanol in terms of energy per unit mass it isn't the peak and is somewhat false in that respect... you don't really get 3-4 miles off a pound of gasoline, you get 3-4 miles off a pound of gasoline and a pound of oxygen. Hydrogen gets about 140 Megajoueles per kilogram whereas most petroleum products do about 40-50 MJ/kg, Fat comes in around 40 MJ/kg itself, firewood, carbs, protein all come in around 20 MJ/kg, batteries tend to do about 2-10 MJ/kg... gunpowder is actually only around 3 MJ/kg but is handy because it burns very, very fast... uranium is 20,000,000 MJ/kg, fusion does a good deal better and anti-matter 180,000,000,000 MJ/kg

No, a cylinder's more efficient for getting a symmetric burn on rocket fuel and there's only so many shapes that are structural sound and minimize the mass/surface area of an object. That's about the only reason rockets tend to be cylindrical.

That's like saying knife or kettle technology has increased at a snail's pace. Rocket's are comparatively simple devices, just like guns or cars or knives they are so immediately practical that once you have them you max out the design pretty quickly because it's important. Radio hasn't improved much since it was invented either, just minor tweaks or taking advantage of computers.