Thanks for the suggestion! This has been a tricky aspect of the design for sure. As it is now, the game weights the random ability selection pretty heavily towards your current class's "native" abilities. The shop algorithm is also weighted so that symbols that your class is associated with (shields for the cleric, for example) are more likely to appear.
Making abilities and shop faces line up perfectly with your class's needs would certainly make builds stronger, but also less varied, and you wouldn't get the chance to discover new cross-class ability combos as you play. I also like the small challenges that occur due to variance, such as "I just got Fireball from a lore chest - how can I modify my Cleric build so that I can actually use it?".
Even if "no cross-class abilities/symbols" was just an option, it would still be strategically correct to always have it turned on, and I'm wary of providing an alternative that is strictly better but (in my opinion) less fun for many players. I will keep thinking about this, though, and there may be tweaks in future updates.
Thanks again for the feedback!