I’m surprised that you talk about “World of Caster” when to me it feels things are heavily in the favour of Melee classes, and rogues are a premium M+ class - but then again the real content I do tends to be more pvp based than pve, so I can’t speak for raid viability.
To try and actually answer the question however, combo points happen way faster than shards.
Shards are made up of 10 shard fragments.
To use destro as the example, a chaos bolt takes 2 Soul Shards to cast and hits hard. A single cast of incinerate, your main filler spell, casts 1 Soul Shard fragment (2 on crits). A single cast of conflagrate, your set-up spell, generates 5 Soul Shard fragments. So when you’re using your rotation properly, you need about 4-5 casts per Shard, meaning 8-10 casts per Chaos Bolt.
As a rogue (I’ll use assassination as an example because you’re specced into it now), your finishers take 5 combo points to max out and hit hard. A single cast of mutilate, your main filler spell, generates 2 combo points. A single cast of garrote, your set-up/maintaining dot, generates 1 combo point. So when using your rotation properly (I think) you need 3 casts per 5 combo points, meaning 3 casts per finisher.
Bearing in mind no rogue abilities have cast timers but warlocks do:
- Warlock takes more casts to build up to the spells were actual damage is.
- Warlock takes longer to get those casts out.
Lucid Dream essentially halves the build time for casters. For rogues, it lets you get more abilities off in a smaller amount of time but doesn’t change the CGD limitation.
Although I can see how having your mutilate build 4 combo points would be a really fun playstyle, I can see why Blizzard balanced it the way they did. Finishers every other ability would be insane. Is that a problem? Mm. Possibly not. It might make rogue Tier 1 but there’s nothing wrong with that. But they balanced it around energy rather than combo points for that reason.
Hope that helped; sorry it probably is not the answer you were wanting, but it does make sense.