Star Pact is way to similar to Stormcaller Pact
Both names use ‘Pact’ as a name.
Both skills give +135% electrocute damage and +135% frostburn damage.
Stormcaller Pact gives 15% weapon damage to Lightning
Star Pact gives 15% weapon damage to Cold.
Stormcaller Pact gives 13-36 electrocute damage for 3 secs
Star Pact gives 27 frostburn damage for 3 secs.
These two skills are a SHAME in terms of innovative mechanics.
Please change them as soon as possible to make them different.
Stormcaller Pact gives 15% weapon damage to Lightning
Star Pact gives 15% weapon damage to Cold. <This is hardly the same thing 
I count this a s a difference not similarity.
Another differnce is that one gives a powerful reduced CD, up to 15%, that works well with everything: Trozan shard, Shadow Strike, amarasta BB, etc. , while the other gives up to 50% Crit damage. i’d call that a pretty big difference as well.
What puts you off probably are is the %lightning, cold and Frostburn damage, but you need to bare in mind the skills they were designed for.
Storm Pact is for burs damage on attack skills which are spammable, or on totem or wind devil which are fire and forget. Star pact provides consistency for CD skills like Shard.
The fact that both have the word “pact” at the end, don’t know what to tell you there:D
One is for Lightning and the other is for Cold, enough difference for me. Plus Star Pact has CDR which is awesome.
Maybe some different mechanic for each one would be best.
Both are exclusive skills.
Like Crit Damage and CDR? 
Not as cut and dry as that, and that’s the point. Depends entirely on your build. Star Pact would let you get more skills out more quickly. Stormcaller’s Pact would make you hit harder.
My two cents:
Star Pact uniquely adds CDR that synergizes well with skills that a cold or lightning caster are likely to pick up such as Trozan’s Sky Shard, Olexra’s Flash Freeze, Wind Devil, Storm Totem, Amarasta’s Blade Burst, Ring of Steel, Blade Spirit and so on. And that’s not including the fact it allows defensive skills like Mirror of Ereoctes, Blade Barrier or Pneumatic Burst to be used slightly more often.
Stormcaller’s Pact offers a nice chunk of critical damage and a chance to inflict a large amount more of Lightning % on attacks that allows you to do more damage with high OA (or a way to strip DA such as Flashbang) resulting in more sporadic increases or bursts in DPS.
Edit: Beat to it :D.