there are some things that are so good that you should have them, yes. for example, pool powers for optimized builds are usually "travel power, hasten, leadership, fighting" or some minor variation
but otherwise there is a huge amount of flexibility in how you slot, and what powers you pick. nobody's going to force you to slot the knockdown enhancements, but it's a really good idea to do so, just as it's a really good idea to stick an Achilles Heel proc in every -def power
this isn't really WoW where you must have this build or nobody will bring you to raids. don't worry about being able to do what you want