I thought the primary objection was fast in, not fast out.
I've never been worried about planet busters, mainly because I consider that only a few ships are actually narratively capable of doing that. When I think of ship railguns and torpedoes, I see them packing power on a scale capable of devastating cities and not cracking planets open.
Even with the Battle of Yamatai, there were plenty of ships capable of leveling their anti-ship weapons at the planet itself to lay waste to it. And yet, ultimately, what was more hazardous were ship crashes on the planet (with the Miharu crew ultimatingly failing in stopping the Mishhu flagship to make a suicide run at the planet and crash in a fashion that caused a lot of surface damage on the planet).
And, honestly, that seems to be consistent narratively. SARP's history is one of specs having big numbers and the application actually being much weaker. If a ship can survive an attack, there's no reason whythat same attack should be expected to crack a planet open.
And, besides... historically, "sun busters" have been far more of a danger anyways. And they typically manage that through plot-sciency-weaponry.
EDIT: Thinking of this from an OOC perspective, before taking into consideration any physics and such, what if we basically had a 'scout rule' where individual ships below a certain class/size could leave quickly, but larger ships and fleets could not and were more committed?
Well, we're kind of all across the board on that.
-For example, the genesis of the Plumeria's design - the Sakura-class - was to be an interceptor. Intercept enemy forces before they get from point A to B.
-Then there's the unwritten rule that Wes' ship design is the fastest in the universe, regardless of rhyme or reason.
-And then there's a statement - I think Uso made it - that bigger ships are actually supposed to end up being faster than small ships, and therefore it was not actually possible for fighters and scout ships to actually range out and outrun other slower vessels. SARP's notion that every ship must be as fast as possible anyways kind of threw a shoe into that. Then there's the speed scale that came later which standardized that (save exceptions, see above) but also made variations undesirable.
In warfare, it'd totally make sense to me to have lighter ship pickets made to intercept scouts, with scouts coming in, taking a look at the disposition of the ships and then sending word back so that when the bigger ships would FTL in, they'd be in the best possible posture (and thus not that badly positioned if they did commit).
But, then again, KFY sensors are so ludicrously powerful that scouting is actually of limited worth. Again, that's a vestige from the Ayenee period where higher numbers were better, regardless of what they actually entailed.