Inconsistency in mandatory targets

Alright, so it's probably not the first time this problem is being raised, but HOU blew my mind as to how inconsistent it is when it comes to mandatory targets for spells. 
A little about magic rules first. In paper magic, targetting works as follows:
- You cannot cast your spell unless you can target everything the card instructs you to. For instance, Cone of Flame needs three different creatures to be able to cast it. Similarly, you can't cast Tribute of Hunger if your opponent has hexproof (though you can cast Thoughtseize on an empty handed opponent because it doesn't target the card but the opponent).
- As the spell resolves, it checks for at least one valid target.
   > If there are no valid targets, the spell fizzles. For example, Lifecrafter's Gift instructs you to target a creature first. If that creature fizzles, the entire effect fizzles, so you won't get to put +1/+1 counters on the rest of the creatures with +1/+1 counters on it.
  > Interesting enough, Cone of Flames will still resolve if only one of the three creatures it initially targeted are still on the battlefield as it resolves (because it has at least one valid target).

Now back to MTGPQ. I noticed two spells so far that completely baffled me when it comes to MTGPQ mandatory targets:
- Doomfall both exiles a creature and a card for your opponent. Although it doesn't target any, both are mandatory (at least one creature on the opponent side AND a card in your opponent's hand). This is inconsistent with past similar spells like Anguished Unmaking that could be cast just fine in spite of the opponent having neither creatures nor supports under their control, and it makes sense! Anguished Unmaking has no targets, neither does Doomfall.
- Kefnet's Final Word targets a creature. In spite of that, I watched our buddy Bolas cast it on an empty board and get their hand drained. You should not be able to cast it if it has no valid targets.
- Similarly, although I know people will not like this for balance reasons, the way Bolas' ability is worded now, it should be able to fire it in spite of the opponent not having creatures onto the battlefield or cards in hand, since it has no targets.

I could argue as to why Market allows you to draw cards if you can't discard although Cathartic Reunion did not. To make these matters even clearer, I think you could introduce wording for "mandatory costs" for effects like these - if you specify them as such on the card description, you eliminate ambiguity.

Bottom line, I think halfway the problem is of wording and halfway of implementation that with some rigor and focus can be corrected.
Cheers!