Whoa this is getting grindy and really, really confusing. Lvl30 Artisan/Lvl30 Warrior, and now I'm supposed to find and kill a Slave Driver to advance past lvl30 Warrior, who is a unique boss monster that I've already killed for the main quest ??!
I keep having to get back to the town to heal up after every few encounters on lvl5 esp. ants, dreks and spellcasters, but I can cruise lvl1-4 forever and stay full hp. WTF is this balance.
Also the fact I can't just buy expendable healing items in this game really, really bugs me.
I went mixed class just because apparently it's how things are done? But now I'm having serious doubts. Might just restart my Giant with pure Warrior and get Explorer along the way, since Artisan seems not particularly useful for anything except opening chests. (FUCK you spinners!) Or, even better, I'll make a Cleric or something since having to go back a 100000 times to heal up isn't fun.
While there is truth to some of what you say (the game is a massive grindfest and it becomes one even more so as you progress), the main reason you are having the trouble you are writing about is that you are a novice to the game. Here are a few tips to help you on your way.
First things first - YOU NEED A PARTY!!! It needn't be big in the start, but having at least two diverse characters going in at the same time is essential. Eventually i managed to buy ascension and started playing from the top. I now have two characters who always travel together - a lvl 15 saris thief who i will dualclass into explorer, and a dwarf warrior who i will dualclass into a cleric. These two characters alone give me immense diversity.
Let's take the most obvious and possibly the most beneficial plus - they both have daggers of stealth, meaning that my party of two gets FOUR HITS PER ROUND, slicing and dicing through pretty much anything lvl 3 can throw at me. The dwarf is a good tank, meaning that i can switch him to the first slot whenever the thief gets low on hp and he can take the damage. The thief on the other hand can easily open 99% of the chests without getting my party teleported, burned, aged etc. Now, imagine if you will, how wonderful they will be once they have 30+ lvls in their 2nd class - the dwarf will be able to restore hp, heal wounds cast spells to dmg the foes, and, most importantly, he will be able to resurrect others in the dungeon. The thief will be adept at mapping the dungeon (when she sees a pit in front of her it will be registered as a pit on the first or second glance, and won't take an eternity like now), moving around the dungeon, both by casting levitate on the party and by porting it around etc. I trust you get my point. Add to this the eventual mage i am going to make, who will charm the monsters they meet... it shall be grand, and more importantly, much easier than soloing the dungeon.
I know there wasn't much chance you could have known this, but the warrior doesn't need to start as an artisan. The artisan's guild is primarily there to help you set up a not-so-squishy caster character until they are lvl 30, as the artisans bestow the most hp, except for the warrior's guild. I won't insist on it, but if you ask me, making a new, pure warrior who you can later dual class into something other than artisan is advisable.
As for the dungeon itself, it gets exponentially harder every 2 odd lvls, so 5 is much harder than 4, 7 much harder than 6 etc. If you are frustrated now, wait till you see your first nostrum, which will stone you with one hit, leaving you to always loose a point of con during the raise.
This is why you need to prepare. The game gradually introduces you to new concepts. While you might have managed to survive on brawn alone till lvl 4, going farther will require some planning, be that as item investment, or making a nother character, which i encourage you to do.
As for your slave driver problem, quest mobs don't disappear from the game when you complete a quest. If he was the end boss of the slave quest chain, he will probably be in the lair again. If he is the same as the slave mashers, but stronger (i don't really remember the tiers any more), you can find him as a random encounter.
Lastly, for now at least, don't underestimate the offensive spell caster. Sorcerers are glass cannons, but well worth it in the long run. For instance, their starter dmg dealing spell affects 2 monsters in 2 groups, a total of four monsters attacked and potentially killed... at lvl 1! Add to that the utility spells you get later on, especially with the wizard, and you have yourself one versatile if fraile asset.
That's it for now. If you have any more questions, feel free to ask.