They are also rarer than NPC AI - which makes them a negligible threat most of the time.
Surely it depends when and where you play? Maybe for you it is regional or you play at an unpopular time which is why you are not seeing other players in open however whilst some random corner of the bubble may be empty, IME as soon as you get near the engineers, or a CG area or a popular thargoid target then you will see plenty of other players, and at that point the chances of meeting a murderhobo, or player bountyhunter/pirate with a heavily engineered ship increase dramatically.
That isnt to say i am in favour of special perks for playing in open or features locked to open.... not at all, people play for enjoyment and just because i do not enjoy playing with random players does not mean i want to be locked out of content.............. but it is potentially riskier.
I generally do not play in open but when i did join open to kill some thargoids it was barely 5 mins before i was attacked by a player. Thankfully my flower picker is tough as nails and he could not make a dent.
OTOH in solo of course you dont get other players watching your back. i shudder at the idea of trying to take on a hydra on my own. that would be way harder in solo than in open with a group of players.