In order for Arcane Savant to have an acceptable power level, you need to intentionally neuter instants and sorceries in your format. If you look at instants and sorceries in CN2, the
only card that's a clear cheat target for Arcane Savant is
Expropriate which,
conspicuously, is also blue. The other spells that seem
overly good as targets are either cheaper (Show and Tell, for one) or draws you into the appropriate color in order to make the most use of its effect (
Selvalla's Stampede).
Conspicuously absent are any cards that could easily abuse Arcane Savant's potentially powerful ETB. The only ways to "easily" repeat a creature's ETBs in the set are:
•
Followed Footsteps
•
Into The Void
•
Kaya, Ghost Assassin
•
Repulse
•
Stunt Double
Note that
all of them are effectively 4+ mana when used on Arcane Savant, and none of the ones that let Arcane Savant stay on the battlefield are instants or sorceries. Oh, right, and special mention goes to
That card
would have potentially resulted in an brutal "one card combo" with Arcane Savant, but the set avoids it by having a grand total of
one way to sacrifice a creature at instant speed, in the form of
Altar's Reap.
If your format deviates from those restrictions (by, say, having powerful expensive non-blue instants/sorceries, or a cheap way to repeat ETBs, or
both reanimator spells
and repeatable sac outlets, or...), Arcane Savant is
probably going to result in an undesirable play experience. Any card that needs
that much babying is
very much a bad design, and
demands to be referred to as such.
...
Because, in all honesty?
That's what people actually mean when they say that a card is "broken" or "poorly designed". They're saying that, barring a
meticulously designed format (which may or may not actually be possible to construct with the Magic card pool), that card doesn't lead to fun times. And, oftentimes, people will
defend that description if asked, usually by mentioning
why they think that a given design is unacceptable.
Going "but you can make a format where the card isn't broken, so you can't say that it's broken" is
unhelpful at best and
malicious at worse, like going "we can't mention that the Pinto
fucking catches fire if it gets rear-ended, because it's a solid car in contexts where it
isn't being rear-ended!"
And, I say all of this as someone whose
primary interest when it comes to cubing is designing formats that
intentionally violate the normal rules-of-thumb for whether or not a given card is "good", "fun", or "soul-crushing".