...they do enjoy an advantage. but i cannot see why it should be found an unfair one. please share with us your rationale for making such a claim...
Incumbents get access to lists of constituents and get free mailings of newsletters and announcements etc.
They can procure gifts to their constituents that enhance their electability such as job training grants, public works projects and keeping military bases open.
They have the ability to reward local citizens with appointments, grants, scholarships and awards.
They have a staff that helps people having personal problems with government proceses. (i.e problems with obtaining a passport)
They get their name in the newspaper almost everytime they send out a press release (created and distributed by their taxpayer-paid staff) boasting of an accomplishment.
They get their name in the newspaper almost everytime they make a public appearance or meet with a VIP.
They can claim co-sponsorship credit for legislation that they did not do any work on.
They can reward their friends/donors/allies with jobs and appointments to advisory bodies, commissions etc.
They can reward their friends/donors/allies with legislation that provides grants, loans, government contracts and exemptions to regulations etc.
They automatically assume leadership positions in their political party.
Their political party will almost surely support their re-election, even if there is a pretense of having a primary election or other process.
Their name is listed on the ballot as an incumbent, almost guaranteeing a vote from lazy and/or uninformed voters content with the status quo.
They are given awards, ceremonies and have public works projects named after them by local politicians seeking favor.
They can access high paying and/or prestigious speaking engagements, guest editorials and book contracts.
All of these benefits are considered perfectly legal and even ethical, if done with a veneer of legality. (i.e. obscuring the connection between a campaign donation and a legislation benefitting the donar.)