Look, I'm seeing this purely from the perspective of a new player, getting insta-killed when they aren't taking any obvious risk. Or, really, any player doing their own thing that's not AX Combat related. The game needs to give players more fair warning when undertaking specific mission type that put them at a greater risk that's not obvious.
There are known risks in many aspects of the game, you carry Cargo, there might be Pirates, you carry passengers, there might be a wanted fellow aboard etc. These are calculated risks the player can choose to take, or not. Getting jumped by a Thargoid when not engaged in Thargoid content and not near any of their systems etc. could easily be a rebuy event for many. We don't yet know the extent of things, yet OP was surprised by the event, and seemingly not too happy about it ruining their chosen gameplay.
As for me, not really that fussed, might make things interesting. Not what I'd choose, but whatever. Not sure I'd survive in my current ship though lol. I just don't want to see a newer players time ruined by it. I know more people who've gotten into Elite and had some random event spoil it for them, never to return, than I know who still actively play.
Just make the risk clear in the mission briefing at least. We now know from external sources initially of this new danger, let that be reflected in briefings. We don't know for sure how far these encounter extend, nor if they'll expand further.
What if Thargoids start going after miners next? Active targetting explorers way outside the bubble, because of "narrative"? Just a little warning is all I suggest, for the children... erm, new players lol.
To reiterate, I like random events and surprises, with the Thargoids behaving differently. To force that on players not wishing to engage in that content though, by actively avoiding Thargoid space, is a bit much.