Some companies have structures for internal advancement. New writers might have to go through a probationary period before being allowed very much responsibility. As writers demonstrate competence through their performance, they are given access to higher-value orders and sometimes more lucrative compensation. Being a "senior writer" probably indicates that they have spent enough time with a company to have advanced a bit.

I'm new the site and have only been writing essays for a little over a year, but the proliferation of substandard writers and companies alike definitely compromises the legitimacy of this business (such as it is). My own--admittedly very limited--experience with other writers' work has been pretty negative. Then again, I work for a company that is apparently not particularly reputable and maybe outright evil so... I wish I had found you guys sooner.

Hi guys,
I'm new too. I've been making my primary income by writing essays for the last six months or so, and have kept myself busy enough that I'm only just getting around to trying to figure out how to track down the community of other writers. I feel like an idiot. But I really am glad to have found you guys!