So if Medical-3 makes one a Doctor.
Does Admin-3 make one a Lawyer?
I think you are trying to do what other editions of Traveller has done (starting with DGP's UTP for CT) and made a level of skill roughly equivalent among all skills.
The rules in CT show that is false thinking.
Why?
The weight of a skill level does not remain constant among all skills throws.
Let's take some examples from the CT rules to illustrate my point...
When making a gun combat attack throw, a weapon skill level provides a +1 DM per level on that throw. You're throwing 2D6, looking for 8+ with a +1 DM per skill level (plus other modifiers).
Switch to the Vacc Suit skill. A typical use of that skill is, when something happens, to avoid that incident and remain in control--to not go spinning off into space. This is a 2D6 roll, look for 10+. But, a character is given a +4 DM per skill level.
This shows how important expertise with a Vacc Suit is when going into freefall. And, if there are no other modifiers, a Vacc Suit-2 skill level makes the task a 100% success every time.
Obviously, a character with no Vacc Suit skill will have a hard time in Zero-G. Vacc Suit-1 makes the character fairly competent. And Vacc Suit-2 makes the character a master in Zero-G that never has an issue.
What happens when there is a engineering problem on the ship? The Engineer character uses his skill in Engineering at a +2 DM per skill level, when he tries to fix the issue.
Next, take a look a the Low Passage rule--the one for bringing a character out of low berth. The roll is 2D6, looking for 5+. A character gets a +1 on this roll if he has Medical-2 or better.
He's not getting a +2 DM. He's getting half that. And, if he's got Medical-5, he still only gets a +1 DM on the throw.
Point being: In Classic Traveller (and in no other version of Traveller, I believe), a skill level in one skill cannot be compared to that of another skill.
When creating a task for a player, the Ref needs to evaluate how important a skill level is to the specific task at hand, then create modifiers based on that decision.
To answer your question in the OP, it is up to you.
For me to say one way or the other, I'd have to know more about your objective. Are you trying to create Lawyer as a skill? Or, are you going to allow skill in Admin to cover whatever you need a lawyer for?