I've no problem with lots of epic conflicts as i like those kind of stories but i agree that it becomes repetitive and depressing when they are placed to close together in the trek timeline. The established trek timeline stretches across several centuries so there’s more than enough room to have lots of these kinds of stories without giving the impression the federation is in a constants fight for its existence
Actually, the epic nature of the conflicts depicted in the books is perfectly in line with what was stated on TV.
Remember in Q Who, before Q flung the Enterprise into the Delta Quadrant, Q himself stated that the humanity/The Federation was expanding much faster than expected. They were moving into parts of the galaxy where they had no experience dealing with the sort of lifeforms that they would find out there. He specifically said..."you compare yourselves to the pitiful adversaries you've already encountered, the Klingons, the Romulans...they are NOTHING compared to what's out there." Picard brushed that aside so Q introduced them to the Borg. This of course was before the discovery of the wormhole to the Gamma quadrant or before Voyager and the Equinox managed to make lots of enemies in the Delta Quadrant.
TrekLit has only taken Q's comment to it logical conclusion. The Federation cannot expand forever without encountering some resistance. The late 24th century has shown the Federation expanding its reach even faster by touching parts of the galaxy that do not even border its space. Now in the books, the Federation has the ability to cross the galaxy in a short time. This should bring them into conflict with more species even faster.