Considering Time Warp,
my mono-Blue deck posted upthread is one of my very best ones in terms of results, and it in no way is missing it. At heart, these decks are aggressive tempo decks, and
Time Warp, while a card that can often be a brutal finisher here, is also a 5 mana card in a deck that
Bident of Thassa apart, curves out at 3, and has very low margins of error.
It's the reason I use
Negate and
Nullify over
Dissolve as 3 mana is too expensive for a counterspell in this deck, in the same way you'd use
Shock over
Incinerate in a Goblin deck, trading power for speed. Making an analogy with Time Warp, would you put a singleton 5 mana
Relentless Assault (as it's only the extra attack phase we care about here) in a Goblin deck? Very unlikely.
If you draw Time Warp at any point before you have 5 mana, it could as a result prove to be a fatal loss of momentum. With counters, bounce and flash creatures, I want to play, or have the option to play, every card in my hand as soon as possible, and win games if needed at 3-4 mana if my draw doesn't come off.
For the most part, Time Warp will lose me as many games as it wins me by being a dead draw when I needed something else. It'll only come out in mana-rich games where either my draw has come off, and Time Warp is simply a win-more card as I'm dominating, or flooded games where it does nothing other than act as a cantrip as I have barely any board, and only stalls defeat by a turn.
A much better card if your plan is to add a singleton to push through an extra turn's worth of damage is
Hall of Triumph as It's cheaper, sticks around, and has a defensive benefit. Sure, you'll only get on average 2/3rds of the damage a Time Warp would offer assuming all creatures get through, but that's acceptable for 2 mana less and often enough. There's also the fact you can also play a bounce spell in addition at 4 mana, or hold for a counter or
Quickling too at 5 mana which makes it a much better card for me.
Lastly, there's also the issue of space. I wouldn't feel comfortable cutting a land for a 5 mana spell, I'm at what I consider the absolute minimum for creatures (there's no decent options or I'd add more), you can't cut the draw element and I wouldn't want to cut the 12 control spells either.
So no. Time Warp is not a missed trick at all in my book, and would in no way be the best card in the deck in the faster Blue decks. It's arguably marginal, but for some would likely result in a net loss of consistency if anything.