I find that both of them have an almost post-metal approach to alternative metal. The difference between them is that Tool focuses on making complex and progressive music, while Deftones goes for a more melancholic style, and at times borders on shoegaze. Still, songs like Digital Bath and Passenger sound like songs that would belong in a Tool. Hell, Maynard James Keenan is in the latter track.
I'm on the fence with Tool's earlier work, but Fear Inoculum was just a bad album. It felt like a insincere carbon copy of their old work. Also Chocolate Chip Trip is just an awful track. Synths that sounds outdated in the worst way possible.
Admittedly there is a bias with this. I find the majority of progressive music to be empty in terms of emotion. It's just people showing off how well they can play. Bands like Dream Theatre and Anathema are just abysmal. Full of cliches and easy metaphors. I tend to connect to music emotionally, and I find Deftones achieves that.