As much as I think 6e/7e was the high point of canonical Warhammer, the power/dispel dice generation rules weren't. The utility of magic is proportional to the amount of spells you manage to successfully cast, and the more power dice you have, the larger a fraction of your spells end up successfully cast, for a given number of opposing dispel dice. Hence, magic in competitive play ended up being an all-or-nothing affair, either you have a bucketload of power dice or you ignore magic and just take measures to dispel said bucketload.
As much as the spell selection of 8e was broken, the power die generation system was far better because, contrary to 6e/7e, bringing more wizards meant diminishing returns as they'd compete against each other for the same largely fixed number of power dice. Or would, if several armies didn't have ways to circumvent that mechanism through additional power die generation.
Nope, T9A is where it's at. 8e system for power/dispel dice generation but without all kinds of ways to break it. Spells that, for the most part, are quite powerful but situational, requiring smart play and not just nuking the enemy with damage spells.