The first Excellency is the Dragon Blooded's 'thing', just like the third is the Siddies'.
You're right in suggesting that almost no DB will take the 2nd Ex for abilities like Melee - This is an intentional design choice; DBs are supposed to go for lots of dice, and hand trouble with auto sucsesses.
However, there are still certain abilities in which Dbs will opt for the 2nd ex. Athletics is my favourite example; Most of the time you're trying to get a small number of sucsesses to not fall, or whatever. Getting many more than the difficulty doesn't really help much.
You're right in suggesting that almost no DB will take the 2nd Ex for abilities like Melee - This is an intentional design choice; DBs are supposed to go for lots of dice, and hand trouble with auto sucsesses.
However, there are still certain abilities in which Dbs will opt for the 2nd ex. Athletics is my favourite example; Most of the time you're trying to get a small number of sucsesses to not fall, or whatever. Getting many more than the difficulty doesn't really help much.