@dragonlike To answer all your question; first you should need to know these concepts;
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Shattered Realm : An area that scales endlessly. You kill 3 map of monsters then go to a boss room of that level, then next-repeat. There is a timer but if you consume it or die a lot; penalty is just less loot. Monsters and bosses in each level are mostly random but their strength is not. You decide to go on or get reward after every boss room. There are ideal farming levels and there are higher levels which is done only for glory, no loot.
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Crucible : An area that you challenge with waves of monsters repeatedly. There are certain monsters in every waves. You decide to go on or get reward in every 10 waves. There is a max level which is 170. People do 130-150 for farming or 150-170 for build testing/glory. It also provides you certain buffs for a time so veteran players use rules like 3 buffs and 1 banner and depend on timing rather than if build finish it or not.
Edit/PS: Crucible times/records are more dependent on player skills than other contents. When you see a good build with good crucible time, the credit might belong to the pilot more than the build. And that kind of piloting can be gained with practice and experience. -
Main Campaign : It’s basically the acts and quests but after finishing ultimate main campaign, there are challenging farming areas. Totems helps beginners to get items/blueprints but there are also rogue-like dungeons and other secret quests. There are Nemesis creatures you can encounter after you reach certain degree with enemy factions.
Edit/PS: So called ‘‘End-game content’’ actually starts within the ultimate main campaign since there are optional areas and bosses that you don’t have to do to be able to finish the questline/act-line. -
We, veterans mostly do not care for normal/veteran and elite difficulty, we try to pass through them just for fast level-up and to reach ultimate because the only level that matter is ultimate. Finishing things in normal level doesn’t mean anything. Though for a beginner it’s all steps, so when you started you should take time and do all content slowly to learn the game. Learn the game, have fun with the campaing before considering end-game
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So for most of us; ‘‘Useless builds’’(as you put it) are only the ones that can’t even finish ultimate main campaign, can’t deal ultimate rogue-like dungeouns nor any nemesis. And that’s caused by mostly wrong building. When you learn game mechanics well, any build can finish those. Ofc good builds can do blindfolded
So skill or class choice doesn’t matter much if you have the knowledge to build around them.
But to be more specific; I believe we can categorize builds in three section;
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Low-tier builds. Those are mostly self-founded/unsynergized weird builds that can finish main campaign, and do rogue-likes with careful playing. They also can do SR and Crucible up to a level but not efficiently. Some beginner build are in this category but they consist only vendor gears.(There are also much better beginner builds) For example my first successful build was something like this. It could finish all content in campaign and do SR 50 or so, was a weird one I admit, then I re-specd it after I learned about the game more
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Mid-tier builds are one step further in end-game. For me it’s basically, being able to do farming range SR. Which is 65-66 or 75-76. Though there is a big power difference with 66 and 76 levels, 65-66 farming is more efficient because it’s faster and provides enough loot. So mid-tier builds can do 65-66 without having too much trouble. They also can do crucible with buffs and banner if you don’t care about timing but won’t be consistent enough. Main Campaign contents are not problematic for this kind of build. Some of these builds can also kill celestial bosses.(not all but don’t wanna spoil that part for you so won’t give you names that matters in build proving)
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Top-tier builds; These builds can do Crucible with certain speed and atleast SR 75-76 with some consistency. Some do much higher SR levels, some do much faster in Crucible. Some veteran players care Crucible more than SR since it’s monsters are specific and there is not much randomness except the mutator debuffs in every wave. These builds also can do serious celestial bosses(but there are certain archetypes for those monsters depending on their damage type)
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So there are also builds that can do SR 100+ and sub 4 min Crucible at the same time. They are kinda extra top-tier. They usually get nerfed by Z after a few patches. I guess they let us have fun with those for a while
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And ofc some playstyles are luckier than others in end-game. So as @Nery said, there is no such a thing %100 balanced game. Grim Dawn is not a game that you pick a build randomly and do everything as same as other builds. There are differences between builds, damage types, playstyles etc. But there is also huge diversity. When I created a character and level it to be 100; if my theorycrafted build was sucks I can easily change it to be something else. Most class combo have atleast 4-5 viable builds supported by sets and atleast 1 really good build option.
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So; now you have some information about game difficulties; Build Compendium as @powbam linked before and check the builds from class by class, decide for yourself. And believe me, compendium has several builds for each class, but there are much more out there, unposted in forum or not sended for compendium.
Last PS: Having fun is much more important than completing the campaign or exploring the end-game content. So just give the game a shot, improvise at start, have fun and try to discover it’s unique features.