Even with save-boosting items scaling more efficiently than Intelligence-boosting items, that last sentence is usually incorrect. Casters boost their key stat, other classes boost their key stats, which aren't always a save stat (and if so, is one of three save stats). Wizards can also pick on a conspicuously low save (eg a warrior's Will save is probably low, a mage's Fort save is probably low). Unlike in 2e, landing a spell on a target becomes easier in 3e.
This is very true. The imbalance between saving throws is extremely notable in 3E. It should also be noted that we're not actually talking about a Fighter vs Wizard comparison here, but a Wizard vs Monster comparison. How do the saving throws stack up for monsters of the appropriate CRs? The numbers tell the story - extremely erratically.
CR 1: Riding Dog (F+5, W+1), Krenshar (R+5, W+1), Gnoll (F+4, W+0)
CR 5: Wraith (W+6, R+3), Basilisk (F+9, W+3), Troll (F+11, W+3)
CR 10: Rakshasa (F+8, W+6), Fire Giant (F+14, R+4), Bebilith (F+16 W+9)
CR 14: Horrid Umber Hulk (F+17, R+6)
CR 15: Marut (W+8, R+6), Classed Vampire (R+16, F+7)
CR 20: Balor (F+22, W+19), Tarrasque (F+38, W+20)
There can be a terrible imbalance between high and low saving throws. This is probably even more apparent with NPC statblocks...
Taking the particularly unoptimised iconic characters from Heroes and Allies (3E, but it will serve), we find Mialee has the following Saving Throw DCs for her best spells:
Level 5: DC 18
Level 10: DC 22
Level 15: DC 26
Comparing those DCs to the saves of the monsters is instructive.
The trick with Wizards really comes down to one thing: preparation. If they go into a dungeon blind, they have to spread their spell slots over a number of contingencies, which severely limits their power. If they know what they're going up against, they're terrifying.
Cheers!