I watched Suits up until she was written out.
To me, she WAS a main character.
A lead actor is a stretch but she was featured a lot.
The thread running through Suits was a guy with a photographic memory but no Law degree blags his way into a Law firm that only employs people with degrees from Harvard Law.
The truth about him is hidden because of his ability to read past cases and memorise them. He always saves the day when they are in court and about to lose a case. Lots of tension. Will he get found out? Will they win the case?
So the fake lawyer is definitely a lead actor.
The other leads are the partners in the firm - Harvey and Jessica and Louis. The fake lawyer and Harvey are the double act who really carry the show because they know his secret from the start.
The partner Jessica doesn't get the screen time those two do - she leaves part way through the series and makes cameo appearances later but she's classed as a lead actor because she's senior partner in the firm.
Louis has a lot of sub plot regarding his personal life.
Two other characters that feature in the whole story thread are Harvey's super-secretary Donna and the fake lawyers girlfriend ....... played by Meghan.
All the characters have scenes with Meghan's character.
She's kind of the loyal helper to all of them.
She isn't in every scene but as far as I am concerned, she is a main character because of her link to that lead actor's character.
When he comes home from work late, she is there to talk stuff over with him.
When he's at work, she is there beavering away at her desk.
She plays a paralegal. She is the fake lawyers conscience, always trying to make him do the right thing.
If any research out if hours is needed, her character is always loyal to the firm and always works hard to help them win the case.
So she's always kind of around.
In the end the truth came out about the fake lawyer, he married the Meghan character and they moved to a new city to start a fresh life.
I think that took 7 seasons ( or 6, can't remember)
Meghan prob gets as much screen time as Jessica the senior partner.
So I would class her as a main character.
I loved Suits. I loved her and I think that's why it took me a while to realise the actress was nothing like the character.
I was fooled for a long time coz Im stoopid, but no longer.
I have seen - not the light, but I have seen the darkness within her.
But fair's fair. Her character in Suits (in my opinion) was a main character.
And her acting was neither great nor crap.
She was good enough for what was required.
to be strategically placed to block out H's view of the proceedings and to save us looking at him! 
sorry
