The test has us with four "shard" bombs and then RSS and ISB, which are basically two more shard bombs. This makes six in total, and that seems excessive and redundant.

Here are some possible ideas for how to address this. I'm not suggesting to do all of them, just that they are different ways to address the issue.

1) Get rid of the normal damage bomb. Not really sure what purpose it will serve in end game, since most bombers probably won't mine packing two shard bombs. It's not a total waste, but if you want to trim down 6 bombs, I'd say that one could go.
2) Get rid of Dark Matter and Splinter Shards. RSS is the same damage type as Splinter, and ISB is the same damage type as Dark matter, so those are covered. Yes, the pure forms do more damage, but the extra effect and damage boost of RSS and ISB, while making them a bit more specialized, kinda makes up for it. You could raise the base damage of RSS and ISB to make the pure ones, and lower the damage boost.
3) Get rid of ISB and RSS. RSS's stun is really a liability. Every time I used it on a trojan, they hurt me. It can be nice, but it won't be missed. And RSS is not now any more effective against fiends than RSS was in the past, so why not just use a pure pierce bomb?
4) Change ISB and RSS so that they are not exactly like the shards. Maybe make them a bit more like the old shards, but not to that degree. Such as, reduce the initial radius a bit, and expand the shards a bit, or something like that.
5) Stick to the four basic bombs, and give each one a status effect (stun for pierce, shock or freeze for elemental, shock or freeze for shadow, and fire for normal).

In any case, whatever you do do, I also find a bit of a problem with the coloration of the bombs. ISB, RSS, and Splinter all look very similar. I think RSS and Splinter should look similar, with the icons showing a different background or just a subtle change like that. But the ISB icon is colored like a pierce bomb, it would be nice if it was colored more like the dark matter bomb.