As an OL in my group i can say that i don't feel even the tiniest bit unhappy about my "loot" at the end of a quest. Indeed it's not much, but it's enough for you to work with and be able to cast your vengeance upon the heroes. I only finished one campaing so far with my group, which is admit i lost in the end but only because it was 5am in the morning and 4 minds are better than one and other reasons (i won't say which), but other than First Blood in act I i have one every single quest, and then because of my mistakes again i lost the Interlude. After that i was indeed pretty much steamrolled until the end of the campaing. But my opinion is not that the OL doesn't advance as much as the heroes do, in fact i think he is more versatile throught the campaing than the heroes are.
Look at it this way, the heroes get to pick a class and a character at the start of the campaing and they play until the end with those, althought they do indeed level them up and get better gear; gear which is always randomly drawn from the deck and can never know if will be of anyhelp. True that you can hoard the gold for a few quests and hope for that overpowered item you were waiting and saving money for 3 quests ago, but if it never drops i don't see how the hero is OP over the OL. The OL on the other hand has a whole pool of spells, monsters, traps and w/e else he has in his sleeve to throw at the heroes at every single turn, and if you'll say "but bringweed, the OL has a whole deck of card to draw from", then i'll tell you that you can reduce it to a number of 15 (most powerfull or w/e you like) if you don't know how to put to good use every card in the game and increase your chance of draw. It is indeed true that later in the game a hero can one shot almost every monster on the map, but he OL should not play to have monsters alive on the map at the end of the day and try kill the heroes, because that is never the objective. The OL should always look at his monsters as a meat wall that can throw a punch at the heroes and make them feel hurt a little step by step. I think that a good OL will always look at what he has and think his moves 3-4-10 turns away in advance and always know what the heroes will do. As the OL, i would say your greatest weapon is not your "advancement" in terms of spells, monsters and w/e else the OL has in hand, but a great mind to help put to good use those means of making the heroes suffer.
Hope this helps, just my opinion on the topic. Cheers.
First of all, please, use interpunctation and line breaks. No offense.
Second, you should try it a few times. You will see, that you will eventually get steamrolled, after the heroes get the three dice weapons in act 2. Just saying.
Get yourself as much three dice weapons as possible and DO NOT LET YOU DISTRACT, than you will win.