Star Ruler 1 made significant strides away from this tired paradigm, whereas this edition appears to be a step backwards.It used to require you to build within a predefined hull - but that was a thing that went away a long time ago.
The only difference between SR1 and SR2 in ship design is we allow your subsystems to be even smaller than they were in 1 and you have more control over their exact size. SR1's default hull had a 15 space limit (with subsystems able to occupy down to 0.12 or up to 4.0 space), SR2's hulls have an internal space limit as well; the only difference is in the numbers we use.
There are no predefined hulls in either game. The idea of a hull, yes, and space limitations, sure - but neither game restricts the actual shape of your ship. SR2 is more restrictive on where you can put things (e.g. weapons must be able to fire outwards without colliding with another subsystem, engines must face left and have nothing blocking their thrust - exception: graviton) but doesn't restrict the overall shape.
The main difference between SR1 and SR2 in subsystem/components is that SR1 was both more restrictive and expansive. SR2 takes a moderative approach - we hardly restrict the player and try to insure that the design system itself is abusable - but we have specifically avoided allowing things like invincible ships, undefeatable stations, and uncapturable planets this time about in the game balance. Support ships are more limited than flagships, which is a distinction that does not exist in SR1, but nothing is stopping you from making a fleet of nothing but flagships but your budget.