が必要 => need; necessary N4
必要がある => Need/Need to N4
[必要「ひつよう」]はない => It is not necessary for A to be done N2
Needs, Requirements
必ずしも~とは限らない => Not necessarily; not always N3
[要「よう」]するに => A. In short/put simply, B N2
Adjectival, Descriptions
要するに => in short; in a word; to sum up; to put it simply ~ N2
なしに(は)/なしで(は) => without; without doing ~ N1
しかしながら => however, nevertheless N2
Things do not match the prediction
たしかに/なるほど~かもしれない => might; perhaps N3
Speculation
なくして(は)~ない => cannot do without ~ N1
しか~ない => only; nothing but N4
だけしか~ない => only N3