Is max level gear you buy off the GTN just as good as gear you get from PvP/Operations?

Yes, no and totally different because gear is based off irating and set pieces and tacticals.

If you want to skip the whole gear grind to get your irating to 306 instantly, then you can buy any 306 rated gear on the GTN to do that. But that gear is generic and doesn’t have set bonuses or tacticals. You also can’t choose you stat mix or customise it. You will also be paying way too many credits to do this.

306 gear is 306 gear, no matter where it comes from.

What matters are the Set Bonuses, Stat Distribution, Amplifiers and Augments. Appearance isn't even a consideration since you can modify your appearance.

I put them in that order because that's the way I think you should develop your gear. First reach 306 by any means, even by wearing the wrong gear for your class. Getting to 306 is the goal, don't worry about stats. Once you get to 306, work on getting the Set Bonus gear that works for your role/build. Then get it's stats balanced, role your Amplifiers and put Augments on.

Its a lot of work, but way worth it.

To OP,

Sounds like you're relatively new here. That's not a criticism by the way (we all were once). So...

First, welcome!

Second, here is a really good guide on gearing (it's the last section) provided by Vulkk.

Third, I'm not Vulkk.

https://vulkk.com/2017/04/28/swtor-step-by-step-guide-to-leveling-and-gearing-up-your-character-for-endgame/

Best, Dasty

Is max level gear you buy off the GTN just as good as gear you get from PvP/Operations?

You want to get empty "shells" and fill them with the appropriate 'mods' - armoring, mod, enhancement, hilt, barrel, augment, etc - to suit your class, discipline, and playstyle.

Prior to Onslaught you just want any old 'orange' gear and at Onslaught (level 75) you want a 'bonus' set.

Don't waste credits on gear with 'fixed' (unchangeable) stats.