But the implication is that there is a universal (physics) law that prevents directly jumping into an empty hex,
If we understand what (supposedly) blocks this in the rules, we can make a judgement whether it's justified.
The original
excuse justification was that jump drives consumed ALL of the jump fuel regardless of jump number (no jump governors) and the default ships in LBB2 for the most part did not have enough fuel reserve to jump more than once.
If your Type-S Scout/Courier has 40 tons of fuel, and consumes 20 tons to jump 1 parsec ... you aren't going to have enough fuel left upon arrival (only 15 tons after a week spent in jump space to get there) in order to be able to jump back to your point of origin (20/4=5 tons of power plant fuel consumed during the week in jump).
By contrast, with "jump governors" in play, that same Type-S Scout/Courier still has 40 tons of fuel, but now only consumes 10 tons to jump 1 parsec. Accounting for 5 tons for power plant consumption during the 1 week of jump, the ship still has 25 tons of fuel remaining and can jump 1 parsec back to the point of origin no problem.
The REAL challenge with jumping into deep space is going to be a matter of astrogation/navigator skill so as to program your breakout point relatively accurately and precisely. If accuracy and/or precision isn't all that important to you, because you aren't trying to "arrive" at a specific location, then "anywhere within the 1 parsec hex" works just fine for you.
I can easily imagine that with "prototype tech" in excess of the local tech level, the necessary fine control is not yet available and so you need to "hit the barn door" of a gravity well rather than being able to stop and breakout just anywhere you please. Under such conditions, "must hit gravity well jump shadow to precipitate out of jump" due to experimental/prototype tech functionally means that you can't jump into "empty" deep space hexes (no known gravity well jump shadow to hit there) and the ship would presumably misjump in some form or fashion. So that would be a limitation of technology not being fully proofed out and developed, along with the necessary computer navigation protocols to be able to "breakout on a dime" where you want to be in the absence of a jump shadow.