I think there is likely to be a difference between how Gisharel would recount their lore to outside scholars and how the Keepers might discuss such things among themselves and the clans. Take the story of Zathrian. Apparently once it came out exactly what was going on there, the elders discussed the whole issue at the next Arlathvhen. A Keeper of another clan puts forward a document giving her thoughts on the matter for consideration. In it she in no way condones his actions but calls it a "crime against nature", even though she acknowledges his "family was torn apart by human cruelty". She then goes on to consider more the mind set of someone who had done that. Now I doubt she would be as candid in her assessment if asked to comment on the matter to a human scholar but might well just state the facts, possibly agreeing it was the wrong thing to do, without being willing to be drawn on the subject. So it is possible that the Keepers are well aware the Creators weren't perfect, as the tale about Elgar'nan does suggest, but they are just not willing to admit as much to outsiders, particularly if they are trying to get them to respect their beliefs.
It is this measured approach that many of the Keepers do seem to display that makes it entirely possible for a Dalish not to rush into drinking from the Well. Even the clan in Masked Empire aren't happy about their Keeper summoning a demon in order to gain access to ancient knowledge. Sometimes it is not worth the risk. My Lavellans have all weighed up the positives against the negatives and it has actually been harder to justify drinking from the Well.
Postives: It is knowledge of the ancient elvhen. It is part of their heritage. Searching out and preserving knowledge is part of their purpose in life. It could help them in their fight with Corypheus. We may need it for other things and there is no guarantee Morrigan is going to stick around.
Negatives: Solas does not want to drink (I always have him with Lavellan in the Temple party). He always seems so interested in learning about the past, so it seems worrying he wants no part of it. Cole (if in party) warns against it. He specifically says you don't want all those voices in your head. Magical knowledge tells you that it is a geas. So whilst it could help against Corypheus, for all you know it might actually restrict you in some way so you can't. Abelas also hints that it might be too much for a mortal to take, so may actually kill you. That is not going to help in any way at all. Abelas has already said "You are not my People", so clearly he doesn't think being a modern elf is going to give you any advantages. In any case you will be bound to the will of Mythal. Whilst Morrigan is rather dismissive of this, you have witnessed how Corypheus can come back from the dead and even Abelas questions whether a god can truly die. Even if Mythal is dead, the spirits of the priesthood in the Well are very much alive. So once again it comes back to losing your freewill, which may not be a good thing either personally or in your role as Inquisitor. Morrigan is willing to drink and seems genuine in desire to defeat Corypheus, so there is someone else available to take the risk. Cassandra is usually in my party and she advises against it. Dorian (my male romance) does not want to drink or lose me to the Well. Whilst part of the Dalish purpose in life is to recover the past, we also have the mantra: "We are the last of the elvhen and never again will we submit". Binding yourself to someone's will is basically submitting to them. So on balance, my Lavellan lets Morrigan drink from the Well.
Mind you, if there is no OGB, so no confrontation in the Fade with Mythal, then it is irksome having to listen to Morrigan going on and on about how wonderful it is she now knows so much more about elven lore. That was annoying, particularly as she doesn't offer to translate those ancient writings for you. Still, we then encounter Mythal and I no longer had regrets.