To balance out Quest cards vs Treasure Cards, just increase the amount of Quest cards you need to complete to get a (random) treasure.
Here's a variant we use.
Unlike the main rules, even the Warlock ending is hidden. You don't get the 4 "freebie" quests at the start. You get to CoC with no quests done? Sucks to be you. Go all the way back (as per "turning back", but adding the home rule that you can do it from CoC if Warlock ending), and start. You do the 4 Quests and no Warlock ending? Boy, you wasted your time.
Meaning, you have to get to the middle region "legit" (having a Warlock quest, let alone 4, at the start pretty much negates the Sentinel). Then, do it 3 more times to get a total of 4 "In case" it's a warlock ending.
Then, on the 5th Quest card, IF you hand it in, you get teleported to fight the LoD. Win or lose, you get TP-ed back to the Warlock's cave. (Since we use the variant of "you loses mules, horses and big followers in the dungeon", this can hurt.
OR, do up to 8 Quests (4 for the possible ending, and 4 for the treasure) and discard 4 completed quests to pick a random Treasure with no LoD fight. You can't do it again if you have a Treasure on your person, otherwise, you can do it all over again, starting at quest 5 since the first 4 are "for the ending."
And, since I'm English Second language and likely lost you all with the convoluted stuff above, just think of it this way...
If 4 Quests gives you a Talisman now, then 8 Quests sounds about right for a freebie treasure. Some quests will take away counters, followers, spells, items, so 8 is about right (for us) to get a Treasure. Too much for you? Pick 4 Quests per Treasure. Too little? Pick 12 Quests. Put counters on a single completed quest, to keep track, if you're running out of Quests for people to do.
That way, you can use the variant, but it doesn't negate the dungeon. Just gives an alternative.