Put another way... we should eliminate sonic builds because they all have 'sonic immunity removal' built in.
You conveniently left out there are very few sonic spells in the game - not enough for a full rotation. So, yeah, nothing is immune to sonic, but without electric and/or cold added to my arsenal I lose a LOT of DPS - and most importantly against bosses, since my biggest single target spells are cold and electric, not sonic. And there are several mobs that are imune to both electric AND cold, by the way, so there are a few situations where I'm out of luck on two of my three elements.
Which class that has access to poison as a main has access to only poison? Alchemists have access to pretty much all elements, if they gear for them. Blightcasters have access to poison, force and acid, wich, look at that, are exactly aligned with one of the Primal mantles...
I play a lot of artificers as well - and gear for fire and force as well outside of electric, just because I almost always will go for versatility instead of min maxing/ specialization - but they DO have immunity stripping currently - you chose not to use it... So it's up to you to be creative and make it work - like I do with my Stormsinger, despite the shortcomings. For example, the Macrotechnic tree you talked about has, hummm, sonic damage...
Again, tough choices lead to variety - right now the top performing caster builds are pretty much cookie cutter style, differing only in how many past lives and/or time and investment put into the gearing. You either build for max DPS, or you're looked at as suboptimal/inferior. Forgive me if I believe working against such kind of thinking will do the game good overall.
Cheers,
NH