What's the difference between ともあろうものが and まじき？


Both ともあろうものが and まじき seem to be used for say that a person in that position
shouldn't act in a certain way because it is not appropriate. However, I'm not
sure if I understood them correctly. Could somebody provide me some examples
to grasp the difference existing?




「Xともあろうもの(者)が」 is used with X that designates someone or a class of people, to
express a strong disapproval/disappointment. 「一家の主ともあろうものが仕事もしないで遊び歩くなんて」 (how
can a head of a household can go out and have fun without even having a job!?)
「者」 is a formal sounding word, and I find myself more comfortable using
「Xともあろう人が」.

Apparently 「まじき」 historically had [a lot wider
usage](https://kotobank.jp/word/%E3%81%BE%E3%81%98-136099#E5.A4.A7.E8.BE.9E.E6.9E.97.20.E7.AC.AC.E4.B8.89.E7.89.88)
but in modern Japanese it's really only used as 「あるまじき」 to mean "unthinkable",
so I think it basically means the same thing as 「ともあろうものが」. For example,
「仕事もしないで遊び歩くなんて一家の主にあるまじき行いだ」

