Both bombs have the same charge time and charging movement penalties. (I definitely seem to recall that ISB had a longer charging time than the RSS, for some peculiar reason.)
Vortices are designed as utility weapons. They suck. Their first purpose is not damage. They are designed to set up enemies so that other weapons can then do lots of damage to them. They are support-focused bombs. (The old shards were damage-oriented only.)
Old RSS did not have stun. That is solely a feature of new RSS.
The reason old ISB was a considerably poorer choice was because a) its damage bonus was against a family that it was already at a damage type disadvantage against, and b) its charge time compared to its cousin RSS.
Let's look at the two vortices:
- We have the Graviton, which does shadow damage, and used to be the only option with regards to vacuum bombs. It sucks stuff, up to Trojans at its 5* version. It does shadow damage. The only caveat is that it flings enemies outwards after the duration expires, but there are ways of getting round that - shock and freeze infliction, for example.
- Then we have the Electron, which does elemental damage, and has a shock status. This makes it a somewhat better version than Graviton, but not especially so, and it takes more effort to acquire the recipes (non-tradeable Krogmo recipes, 300 coins to get all three). It is somewhat less likely to fling enemies than the Graviton, but the difference is reasonable given the extra effort put in to acquire them. Graviton is not made redundant by the existence of Electron.
The situation is nothing alike.