The phrase "a mere servant" is correct and usable in written English.
It can be used to emphasize the insignificance or low status of someone in a particular context, often in a dismissive or derogatory manner.
Example: "In the grand scheme of things, he saw himself as a mere servant to the powerful elite."
Alternatives: "just a servant" or "only a servant".
He was a mere servant of a public mission voted, paid and cheered for by the American people.
Fassbender's Rochester questions her irritably after she has been hired into his household, curious to see if she will step back and become a mere servant.
He campaigns with Mr. Shater under a banner with both their faces, fueling critics' charges that he would be a mere servant of Mr. Shater and the Brotherhood's executive board.
And Branagh refused to have her referred to as a "mere" servant girl.
Or does he see himself as a kind of Jesuit, a mere humble servant, ready to sacrifice himself to win converts to his religion — to achieve the oneness of all living beings across the universe?
He offered to make William Sovereign Prince of Holland in exchange for his capitulation whereas a stadtholder was a mere civil servant.
Hated how most of the general public treated us, like we were stupid, worthless, invisible – mere servants.
Even though the DCMS team may sometimes look like mere servants obliged to do the bidding of George Osborne, irritating the junior culture minister doesn't seem a particularly wise option when the BBC's future is supposedly under threat.
The best way to achieve both aims is to take agencies out of the framework of financial regulation, and return them to their origins as mere servants and guides for the capital markets.
These are the hallmarks of the emerging American police state, where police officers, no longer mere servants of the people entrusted with keeping the peace, are part of an elite ruling class dependent on keeping the masses corralled, under control, and treated like suspects and enemies rather than citizens.
Religion is a mere obedient and obliging servant of the ruler, his interests and whims.
