If resistances wouldn't be more important in this metagame, Steel wouldn't be nearly as common in OU as it is now. Sweepers raise offensive stats to numbers far exceeding sheer defensive numbers, making resistances key.
Regarding an effective defensive pair, just pair either of the Latis with a Steel-type-Lati@s both resists Fire, Fighting, Electric and Water while immune to Ground, and the Steel-type resists all other types, including all of Lati@s's weaknesses.
Now to another question-what stats matter more, HP or defenses? Take a look at Wailord-it has below average defeneses, but with a generic Bold EV spread takes physical hits better than Vaporeon, and with a Calm one special hits hit weaker than on BulkyGyara! An opposite example would be Dusknoir-it couldv'e been so much bulkier even with an average HP stat!