(Thank you for the freighter list and your thoughts, too!)
I'm happy that Goumindong and Wyvern touched the subject of combat freighters, because that's something I'd really like to see changed (I have faint memory of complaining about this before, but I presume nothing came of it - otherwise I'd certainly remember it). Namely, combat freighters suck for three reasons.
One, they're spreadsheet ships that can't compete with dedicated ships on the grounds of efficiency. I'd rather have a freighter and a combat ship instead of two combat freighters.
Two, combat freighters aren't really all that good at fighting. Not to mention they're pretty much confined to being defensive ships, since they just don't have the capabilities (in weaponry and flux stats) to push offensive. I'd rather have a combat ship that can both defend and attack instead of a pair of combat ships that can only stall.
Three, they're freighters. They have cargo inside, lots of it. That, if happens to be supplies, you'd rather use to repair after combat, rather than lose it in combat, and use the now-free space to take loot. Not deploying combat freighters means less risk of losing both what you already have and the cargo space for more cargo.
The only situation where it's advantageous to have combat freighters is retreating, but even then they can ruin your day by not retreating quickly enough.