Agreed 100%, a well designed game is a game where you need to think a little to find everything, but the logic behind is not twisted. A well designed game does not punish the player who just want to advance the story with item they will not be able to get later, and it does not punish the treasure hunter who do every side quest before the main quest (with a main quest too easy after that).
I think this would be a purpose for a paid game guide, that would be well made and obviously not give away spoilers. I honestly never bothered with paid guides or walk-throughs. I like the feel of discovery, wonder, and figuring it all out on my own. I think really amazing weapons and gear should take effort to obtain or find because I would get bored if it was too easy. I kinda dislike when everything is laid out for me. I do however think there should be a warning in the game. A warning and/or counter that will let the player know there is still more optional quests or items. I think the player should always be able to go back to locations and maybe the optional quest becomes harder if it is done later, but that might take more programming effort and time. Also, this might be different depending on the type of ARPG. Does the player only get stronger with weapons, more heart health or does the player have the option to increase stats without them? This would be a Fable vs Zelda question.
I do however dislike that there are optional quests that are not able to be done. For example, at the start of Fable there were optional quests besides the giant queen wasp. Not enough renown, and I went and got enough. The optional quests just vanish. I put real effort into be able to do those quests and avoided the wasp queen to do it. I wanted to fight that ice troll! This might have been due to bad planning at the start of the game.
I stopped playing Fable after the 3rd game, but I like how some quests were able to be done over and over again. They needed more spice though because I do not like quests that are exactly the same.