I think I’ve address why I think sorc is in a good place, but I’ll go ahead and answer for why I think the 1s shield would be broken (Dee can feel free to elaborate):
Just from a theory standpoint, there are currently 2 classes that have access to inv, and both are melees. There is an inherent power balance here as they are forced to get closer to bosses to deal their damage, so it makes sense that they will eat more shots and in turn might have need for invulnerability. Classes that have range like sorc don’t have to get close to deal solid damage and so shouldn’t need to worry about invulnerability as they should be able to see shots coming and have plenty of time to dodge while safely damaging.
But far more importantly, a change like this would be easily abuseable on Sorc’s ability. Scepters have a low mp cost tied to a class with a hefty amount of available mana which is already very wis-hungry. Oreo has a 5s cooldown on a high mana-cost item that provides other buffs (as is common on seals) during the invulnerability downtime. Cshield is tied to a class that has with a moderate mana cap and low wisdom. It has to re-orient it’s entire set to accommodate for and effectively use the invulnerability. Can it go for a while? Yes, but it is highly susceptible to interruption and is best used when you are literally standing on a boss (and thus are very likely to get hit by any “interrupting” projectiles), making effective use highly reliant on enemy knowledge. Furthermore, it slows and requires pretty significant downtime after it is used for mana to be regenerated.
Now consider: you are proposing 1s (pretty innocent, right? that’s short!) of invulnerability to a class whose abilities cost between 70-80 mp on the most used ones. You would easily be able to spam your scepter for over 5s of invulnerability not counting pets. All of this from a range where you shouldn’t have to worry much about any specific silence or quieting shots. I think we can all agree this is a little ridiculous.
The solution to this is of course to introduce cooldowns to scepters. But do you really want that from a damaging ability? We don’t have cooldowns on spellbombs for a reason. People want to spam their ability key to get their damage in during vulnerable phases. This just fundamentally works against what sorc is trying to do.
I think I get what you are going for (and again, I think a limited-hp shield based on something as a ut would be really cool!), and I hope this didn’t come across as just blatantly aggressive, but this really would not work.