Another reason to actually give rewards for offline play, is that the antagonists can be given a group of raiders that don't even total to a third of their level, giving them close to free run of the mission. But the no rewards for solo missions give the players kind of a crappy choice, wait a long time to get into a mission to have your ass handed to you by a 5-times your level antagonist, or play missions for low gold rewards and no progression given for time put in. Honestly, that will lead people to not play the game again.

The way I see it, there are a few options to make the game more enjoyable for newer players:
1. rework the melee attack system to shift the balance more towards the attacked individual (because having antagonists just run around spamming the melee key is way too op)
2. do matchmaking off of player level, rather than MMR (MMR seems to be based off of success, player lvl is based on experience)
3. rework the antagonist spawn timers to give slightly longer respawns to the antagonist (to help combat the attacker-almost-always-wins melee combat system)
4. give the players that don’t ragequit cause of a way too effing overpowered antagonist a sizeable buff to combat the fact that the antagonist then has close to a free reign on the mission
5. and the simplest of all, just slightly nerf the antagonist. They already have all the advantages (help from bosses, numbers advantage, a not uncommon experience advantage), so nerfing the antagonist themselves would be a good way to give the raiders a chance against a melee-spam antagonist