I like them both. I'll use Sasha if I know I'm going to be facing other heavies, but most of the time I prefer Natascha because heavy isn't my main class by any stretch. When I go heavy, it's because my team needs the class more than it needs another engy, demo, or whatever I might be better with.
This isn't to say Natascha is a weapon for noobs. Rather, it's a great weapon when you don't want to be front man mowing down all the opposition. Instead, it's a support weapon that makes it easier for your surrounding teammates to kill faster and more efficiently. Complaining that it doesn't have killing power by itself is kind of missing the point.
That said, I do like the idea of decreasing its spinup time or slowdown effect.
I think the problem is that performance differences between the two are negligable, Sasha in itself is a support weapon, and more likely to get the kill compared to Natascha, be it direct or assist. I'm not necasserily saying that the heavy needs Natascha to have a higher chance for direct kills. But the damage done by Natascha is possibly too small to be of much worth when as a whole, when taking into effect the rest of your team in a game, Sasha will result in more damage dealt to the enemy, reducing their effectiveness to regroup. The slow down itself is of little inconvinience, and when you're close enough for it
to be annoying, Sasha would have killed you anyway. Unfortunately, in most cases, Natascha will end up getting you killed.
For most weapons that kill me, i get a real sense of "well, they were using the right weapon for the job there. Sucks to be me. If only they were using their other weapon i might have survived". They provide a real alternative play style. Where as Natascha feels like "well, i would have been dead in that situation anyway".
Sitting back and applying annoying spam is fair enough, but done just as easily with Sasha. Sitting back and being annoying doesn't quite work when your damage output is drastically reduced. I never see a Natascha wielding heavy as a real threat. They probably wont kill me unless they get crits or a lucky accurate bullet spread, either of which end in the same result with Sasha. If your team was in a position to kill your target when weilding Natascha, they were in a possition to kill them if you were wielding Sasha. But additionally Sasha provides you with more personal protection, whilst Natascha provides the enemy with more time to shoot back at you before (and
if) they die.
I see it 1000 times like this:
Sasha does X amount of damage to an enemy, someone flanks and kills them with a rocket as they retreat.
Natascha does X amount of damage to enemy, someone flanks and shoots them with rocket but they survive, and require another accurate shot to kill.
Basically you're providing more chances for the enemy to luckily escape a killing blow, or kill you first. Most people are used to accounting for class speeds and -25% means nothing for the brief amount of time that it is applied.
They've failed to emphasise the weapons intended role.
Something like no crits, -25% damage dealt; for 100% chance to slow enemy on direct hit
and surrounding enemies OR lengthen the duration of the effect for +5 seconds OR allow bullets to penetrate through several players. To emphasise the effect of the weapon. Because although the minigun has a wide spread, most bullets
do miss, and a single bullet can only hit (and subsequently effect) one person. In this scenario, the heavy would be better for mass crowd control. Rather than picking out individuals.