Personally I don't really see discard as a means to an end. I tried building discard-focused decks notably with
Mind Rot inside and I don't think it's really that efficient in this meta... We lack other good (and faster) discard spells to really build a competitive deck around that, and the same problem exists more or less with land destruction. If you focus on destroying your opponent's hand and can't do much else in the meantime you are likely to lose and as you said there are ways to get around discard. This is why I don't really like cards like
Mind Rot or
Demolish that have no added value besides hand/land destruction.
The
Liliana's Specter +
Peel from Reality trick is just a cute little combo that may or may not be useful depending on whether or not the opponent has cards left in hand, but it's not really essential. This deck wins mainly through buying time by slowing your opponent's board until you can bring the big threats as well as replaying ETB effects for various purposes when necessary. Discard here just helps supporting that by forcing your opponent to make choices and limit his options, and if you can completely exhaust his hand, then the better but personally I don't always count on that. If the opponent wants to hold on playing lands to get around discarding then discard-focused cards indeed won't do much... But unless we are already in the later game this strategy also slows down his own development which is exactly what I am trying to achieve.
Also
Cultivate is most likely the card I will take from someone's hand if I have a
Brain Maggot not only for the reason you stated but also because most decks running it kind of depend on it to get their game going and I still have other ways to deal with big threats later.