That's the point of a bigger ship - you can't defend your butt against a smaller faster opponent without wingmen or turrets. It's completely fine that way.
Forgot to answer to that

Well, OK. Actually I knew that but let's go deeper here, ok ?
I see this in 2 ways:
If you have turrets with even "just" a 4-5 "nerfed" Python, wouldn't that still be "OP" ? I don't need to have my opponent right in front of me, so I just have to boost to be sure he's not toe to toe with me, then turn, turn and turn to be certain he's always taking damage.
Also, if big ships MUST have turrets, I really don't see the point of gimballed or fixed weapon. Why bother letting us buy them if they are useless ?
BUT WAIT. In the other hand, a Viper equiped with 4 rocket launchers or missile launchers is faster than me, so inevitably, he WILL get toe to toe with me to a point where my defense turret will not be able to do anything and I WILL die ! He just has to make sure he got enough shield cell banks with him to keep his shield while he's getting closer to me. And I might not have the time to activate shield cell bank with that kind of attack where in less thhan 2 seconds you don't have any more shields.
Plus, I just can't get away, my python is not fast enough to outrun a Viper or a Cobra.
And if he fails at busting my ass and has no more ammo... Well as I said, I can't go as fast as he does so he flees and that's about it.
What I'm saying here is, as much as I want the game to be fun for anyone to play and also that i totally agree with the statement that a viper or cobra should be able to destroy a Python, I also think the opposite is true. I don't have to flee right away when I see a lone wolf Cobra or Viper because I know that at some point, if he's super buffed with shield cell banks, I might not just be able to win. That's not "skills" for me to just fit 4 missiles launchers, have 8+ SCB ready and spam the hell out of them.
EDIT: AND FREAKING CHAFFS ! Don't forget about them ! With that in mind, my python will just not be able to defeat the lone wolf Viper I described. Just because I'm slightly less maneuvrable ? There's no skill in that. And I'm pretty confident about my fighting skills, I've spent 2 weeks hunting bounty and I have learned a lot within that time !