Whilst this is true in general, Eschalon's system is broken because magic is able to replicate other skills almost entirely. For example, you're better off spending in magic to pick locks rather than build the lockpick skill (as the lockpick skill doesn't allow you to open anything that magic can't iirc). If you've spent those skill points in magic, suddenly you find you have access to various buffs that replicate 10+ skill levels in melee or ranged skills. You can also buff attributes significantly with magic, meaning that you can race directly at the start to the stats that maximise mana regeneration. And so on. You end up with a guy that has full magic, adequate melee and ranged capability that changes to excellent once you apply 3-4 buffs, and the versatility to do whatever else you want in the game.
One conversation I had on their forum was laughable - I was pointing all this out, and that my mid-level (level 10 or so iirc) character was pretty much unstoppable. Some guy got butthurt and stated that my mage wasn't a 'proper' mage who could throw around nukes etc. So I asked him how much mana and mana regeneration (I forget the name of the stat now, maybe it isn't called mana) his 'pure mage' build had, and it turned out to be a lot lower than my hybrid. I think he thought I was lying until I spelt out exactly how to create this overpowered monstrosity at which point he left the discussion.
The devs could have balanced all this in my opinion by rethinking their skill system, and creating 'expensive' skills [i.e. magic], 'average' skills [weapons skills], and 'cheap' skills [lockpicks etc]. The idea being that any character you build has to have broad capabilities in a singleplayer game like Eschalon, but you balance this by making versatile skills like magic cost you much more so the choice is to either get magic or to pick up the individual skills you want to use at a cheaper rate. I think I also suggested removing/depowering some spells or making the base skill able to do stuff magic couldn't. However, with all the feedback from people saying 'omg Escahlon is teh hard !!11!' I think the devs simply didn't see the problem with the game mechanics they'd designed.
Edit: I did a quick google to see if I could find my old posts, and found this thread
http://basiliskgames.com/forums/viewtopic.php?f=3&t=906
It was a poll put up by BW asking what people thought about class balance. In it, you can see the range of feedback from people who thought what was powerful and what not, but the impression I came away with on rereading it is that Eschalon players may think they're oldschool, but generally they don't have a clue about powergaming. Only 3 people out of 44 correctly responded that mages were overpowered, and I suspect this is because most players didn't properly optimise the rules as given to build a real monster.