Your idea that certain spells are simply amazing on any build falls apart when you look at the costs of some spells that are almost universally amazing and others which are niche. Let me give some examples.
Explosive Mines is one of the best spells in the game. It costs 10 RPP.
Accelerate and Wither are amazing on any build. They cost 10 RPP.
Black Hole is a great AOE spell that can severely screw an opponent's positioning. It costs 10 RPP.
Vines are incredible on any build because of them being free summons, but they cost 10 RPP.
Piercing Strike is a Lightning spell that anyone, at this point, can block or dodge. It costs 15 RPP.
Occult/Holy Cannon are 15 RPP each despite being Masters that aren't necessarily good on every single build (compare this to Occult's Curse, which is one of the best homings in the game).
I could go on.
Explosive Mines is one of the best spells in the game. It costs 10 RPP.
Accelerate and Wither are amazing on any build. They cost 10 RPP.
Black Hole is a great AOE spell that can severely screw an opponent's positioning. It costs 10 RPP.
Vines are incredible on any build because of them being free summons, but they cost 10 RPP.
Piercing Strike is a Lightning spell that anyone, at this point, can block or dodge. It costs 15 RPP.
Occult/Holy Cannon are 15 RPP each despite being Masters that aren't necessarily good on every single build (compare this to Occult's Curse, which is one of the best homings in the game).
I could go on.