Not so.
Casting Orbius with a long duration is a dumb move in a duel. Optimal play is to crank power as high as possible, then cast another spell to extend it.
Also, 5x1 stress=!=5 stress.
True enough but that takes two standard actions and can still be broken the first for no damage exchange by anyone relatively even with you power-wise. I assume anyone thinking of taking on a spellchucker has at least one method of dishing out comparable ass-kickery, even if it is narrowly defined by stunts.
Anyway, the real problem is the block. The damage is just insult added to injury.
An 8 shift damage spell launched at a guy with Supernatural Toughness and a Fair defense roll inflicts a moderate consequence. An 8 shift Orbius launched at the same guy is utter doom unless he can get an 8-shift result to oppose it. Which some characters are just not likely to manage, ever.
Granted, the ability to ignore armor is pretty over the top but it does make sense for
this particular spell since it's causing stress via suffocation rather than direct, physical means. I don't see any need to grant it for similar spells unless they can justify it equally well though.
Making this worse is the fact that one can boost spell power very easily. This is limited in usefulness with attacks that need to be aimed, but blocks don't need to be aimed so...
Sacrificing a pair of mild consequences can get you up to a 13-shift Orbius. Which is basically game over. A similar Feugo wouldn't be so bad, because it would still only be control 8 and therefore soakable with a severe and a moderate by our Supernaturally Tough example guy.
Assume that was a typo and you meant 12, 8+2+2 and all. You may not need to aim it but you still have to control 12 shifts or take those over 8 as backlash/fallout. That makes it a pair of milds and a moderate, or four milds, to make sure all 12 shifts are backing the spell when it reaches the target.
On a Fuego that would bump the weapon rating to 12 and control roll to 12 also, minus five for defense, leaving our tough guy having to soak 19 stress. And since we're giving the Orbius guy two exchanges to get the spell fully set, we have to give the Fuego guy another. Assume he doesn't want to supercharge the second and goes for the 11 stress version in the original example. That's 30 (26 after the -4 for armor) stress over two exchanges or the 5th and 7th stress boxes filled plus an extreme, mild, and moderate consequence (not assuming he bought extra consequences from stunts or recovery because that would just draw things out without really changing anything).
Boiling it down to worst possible case/readings, a 12/8 Orbius does five stress boxes plus a mild, moderate, and severe and takes the subject out of the fight for 8 exchanges. A 12 Fuego plus an 8 Fuego cost the same and do two (5th/7th) stress boxes plus a mild, moderate, and extreme consequence. Over two exchanges, Fuego is
far more deadly but you have to deal with attacks in return. Over three, Fuego is likely fatal, assuming you can avoid being pulped in return.
Read Orbius as it's described, blocking no actions but breathing, and you're going to witness a spectacular kicking of your ass using it in a fight because you basically wasted two exchanges, two spells, and a few consequence slots. The other guy may end up going down too but not until long after he's taken you out by just ignoring the spell until you're dealt with.