I'd say yes and no. If you buy an entire system, yes, it should be scienced out to be optimal. However, Hotchkis doesn't sell torsion bars to match their system, but does offer an adjustable rear sway bar. So they are not truly optimized when it comes to wheel rates, but do have a broader range of adjustment than others and they do improve on the geometric alignment of most things. By contrast, the XV L1 set up is optimized to work together, but does nothing to correct any geometry issues.
Buying parts piecemeal could lead to less than optimal results if you do not know how the system works together and how each piece impacts the other. On the other hand, by knowing how it is all interelated, it is also possible to optimize the results beyond what anyone else out there is offering as a kit. It all depends on the goal and each persons personal knowledge. It isn't really difficult, there are entire books written on the subject, but it can be time consuming to find the best srouces and there can be a fair amount of analysis and mathmatics to sort it all out.
In this regard suspension are no different than engines. When building an engine, you can either call up a builder give some specs and expectations, and have a bullet delivered. The other way you can research, discuss, model, pick and chose, and build one yourself. Depending on your skill, time, desire, and wallet, you can either be very satisfied or sadly disappointed by either approach.
