Senior is a nontransferable honorific, as in: it does not translate between organizations. I have had people who were senior in their old organization demoted to junior (aka. they mostly quit) because they could not write a line of code without internet or IDE to save their life, and I have had people come in as junior even though their started programming when they were 12 and could programm circles around most seniors, buy HR decided they had “no experience” after collage (which, in my opinion, boils down to exploitation of cheap labor). I also met a guy who was an good developer but at his company it was a formal requirement to give a talk to advance to senior. Even though he had 15 years of experience at that company non the less, he could never advance because he was afraid of public speaking.
So seniority is at least as much politics as it is skill or responsibility. In my experience, it boils down to whether or not you feel you deserve it. If the answer is yes, then you should see that you get it and that you are treated (paid) accordingly.