When people talk about gw2 balance the main thing they refer to is how strong/overpowered a build is, but if its only a problem when few people play it its not as much of an issue if everyone is able to play a build and make it OP.
A good exemple of balance i would say is something like guardian which is a very easy class but its not the best class, which means it has a low skill floor and a low skill cap. Something like herald has a high skillcap and high skillfloor and most people consider herald to be OP. But if we look at mechanically weaker players, are they really useful on herald? not really, they just die easely before they even have a chance to do anything compared to guardian that can spam alot of blocks, aoes and has an elite that resets all their cds so they can cycle through their cooldowns again before they die.
If we look at this meta and the previous balance patches, necro before the nerfs to sustain was an exemple of an easy and efffective class. tons of sustain and decent dmg and pressure and even 1v1 ability before the nerfs, now its balanced and not OP, same with reaper, reaper is also a very easy spec it dosent have much to it and its balanced because its easely focused and dosent have many ways to mitigate damage.
Now the things that are not balanced, when it comes to how easy it is to play the class vs the reward: condi thief, core ranger, renegade, burn guardian ( only burn , other type of guardians are fine).
All these builds have something in common, they are all very easy to play and are extremely effective regardless of your skill level. condi thief can kill some1 with legit 2 buttons, same with burn guardian. Core ranger and renegade just win 1v1s for free vs most of the builds in this game without having to do much. a ranger can miss all their skills, play really poorly and still win because the pet hits you for 6-7k . A renegade can just drop aoe on the node and full cap most people for free without having to do much.
When anet devs look at balance, always consider the difficulty of the build. you dont want to make the average player good because of a build, and you dont want to do the opposite either, it is fine for easier builds to exist, not every1 has good reaction time or good ping, every1 should be able to play pvp but easy builds should not be the most effective.
it dosent mean higher skill cap classes dont need nerfs, it just means it dosent need as many nerfs as people ask for because they get outplayed but dont realize it. sometimes people think they should be able to stand still, press random buttons on their skillbar and not dodge any abilities and win, and if they dont win the other class is overpowered, you might think its funny but alot of the casual gw2 playerbase actually thinks that way. It dosent even cross their mind they are not playing good and automatically assume whatever killed them is overpowered and needs to be nerfed.
Anet just neeeds to be careful with balance changes and take class/build difficulty in consideration . i still believe herald , holo are a bit overtuned despite being harder to play classes, explosive entrance needs a nerf and rev healing skills need to be nerfed to make up for the fact that it has 2 healing skills instead of 1 like other classes. Theres other things aswelll but anet definitely needs to focus on easier builds first, that way its alot less problematic if 20 people can make a build OP vs half of the gw2 pvp playerbase being able to achieve the same results without much effort.