Wizards are massively high tier 1 even in just Core due to their spell list. Core contains most of their best-of-the-best spells.
Druids are mid-high tier 1 due to the whole package, even in Core; take out any two major class features (spellcasting, animal companion, or wild shape) and they're a high (really high) tier 3.
Clerics...well, they're definitely tier 1 with everything allowed. I don't play around with them much, but I do believe they're low tier 1 in a Core-only environment just because of how versatile and powerful their spells are (also see domains).