I think there's a few 'better' options in regards to 'unfair' advantages of a VSC.
I agree that you could argue that when a VSC is deployed for a very short time, that a driver/car can get an advantage if he can JUSt manage to enter the pit, grab a pitstop and fresh tires, and then get out right before the VSC ends, meaning cars a little behind can no longer benefit from the lesser time lost in a VSC pitstop. I would argue in one fashion, that this is simply racing and there's also luck, but I can imagine that it is something to look into.
the only reasonable solution for such a manner imho would be that in case of a VSC, there is a minimal 1-lap VSC neccesity, meaning, IF for example the VSC gets deployed, that the race leader must complete atleast 1 lap before the VSC gets lifted again, and the race 'restarts' at the finish line and nowhere else.
In other words, normal pitstop: 30 seconds.
P1 race leader needs to make a pitstop, as does P2 driver.
Race leader is 25 seconds ahead of the P2 driver.
Would lose position under normal circumstances, and P2 driver is gaining due to slightly better tires, and would get P1 in both undercut or overcut.
VSC pitstop would result in a pitstop of 20 seocnds.
Race leader could get a pitstop, and come in front of the P2 driver, and keep his position which he under all normal and fair circumstances LOSE to the P2 driver,
who's team and himself simply were doing a better job untill that moment.
VSC gets lifted right after the pitstop, so now, P2 driver gets handicapped and an 'unfair' treatment, since he still needs to pit,
and now the leader has GAINED a 5 second lead over P2 driver, instead of ended up 5 seconds BEHIND the P2 driver in fair circumstances.
If the VSC would however be kept for a FULL lap atleast,
then the pitstop would still be 10 seconds 'faster' compared to normal circumstances, so essentially there is little change as the P1 driver would still remain
with a 5 second lead instead of a 5 second defect, BUT atleast the P2 driver gets the same chance for those BEHIND him, and so would ALL the drivers,
untill the race leader crosses the finish line again.
ANOTHER option alltogether would be, that not only does the VSC MUST be imposed for atleast 1 completed lap at all times and is lifted when track is clear and race leader crosses the finish line, but that if a driver PITS during the VSC, then the difference in time lost must be added to the pitstop time at the box, and gets predetermined before the race.
the FIA will thus calculate how much an average lap will be, and how much an avarage lap will be under the VSC.
Let's say normal circumstances, a lap is 1:30 on average.
now let's concider that during the VSC, the cars must maintain a delta time, and as such, the average lap will not be 1:30, but will be 1:40 instead.
this obviously means a 10 second difference.
The teams that pit during VSC thus MUST wait these 10 seconds in the box BEFORE working on the car, essentially adding a 10 second penalty.
As such, the net result in the first example would be that the result of pitting under normal circumstances or under VSC will bring you NO unfair advantage,
and the P2 driver would not lose his race thanks to a 'lucky' VSC.
the OTHER can of worms that this would open up however, is that this could potentially ruin the race of teammates driving behind eachother and are no long able to 'stack' pitstop since they need to add a 10 second (depending on the track average) 'penalty'. So let's say Norris pits with Sainz directly behind. Normally, Sainz would lose about 3 seconds depending on how fast they change tires. in this case however, Sainz would get double penalty, as he is behind Norris but Norris first needs to serve 10 seconds, then get the 3 second pitstop, and then Sainz can get HIS pistop but he FIRST needs to serve HIS 10 seconds. in other words, stacking up is going to lose you 10 seconds, so you must stay out.
A VSC/SC pitstop ban ruins somebody's race due to other drivers' fault. After all, if you plan your pitstop by lap 30, and in lap 29 there's a SC for 5 laps, then your strategy is ruined, and you get the risk that your tires won't manage and MUST be replaced but you aren't allowed to enter. that won't work either.
In the end, I think the only reasonable solution is this: just keep it as it is.
I personally believe we are only having this discussion because Hamilton got lucky with the VSC, and there are suspicions that this is a deliberate ploy of some 'behind the scenes' deal between FIA and Mercedes as a result to compensate for the 'secret' deal between Ferrari and the FIA.
Let's put on the tinfoil hat and say: Mercedes got word of a foul game between Ferrari and FIA, where Ferrari should have been penalized much harder, then Mercedes threatened FIA that they would take (legal) action, and then the boys sat around the table and decided that whenever FIA gets an opportunity that they would 'covertly' benefit Mercedes so they can get Hamilton a title aswell as help Merc get another WCC title for the 2020 season.
Dumpster sounds so much more classy. It's the diamond of the cesspools.