Ranger - Great job, has a lot of niche uses. Can deal huge damage and stay out of range of AoE's etc. Expensive to gear some of the better pieces (an Osode and E.bow alone will set you back 7 mill on Midgard unless you can get them through your LS). Expensive job to use, which whilst you said not to factor in, is something you really need to take in to account. If you do an ISNM and are asked to come DD (which for you, if you levelled it, would be your only choice) and a Khroma doesn't drop, you will barely make a profit for the entire run, or perhaps even a loss if your drops are really bad. Easier to obtain gear for than other DD jobs as it isn't as heavily dependant upon R/E pieces, you can AH / Assault / quest a lot of your gear.
Samurai - An amazing DD job, great against all levels of mob, and very flexible too. Can be used to Meditate > WS for kited mobs, sub THF to plant hate on tanks, and chuck out huge numbers in zerg situations. Things like Hagun and Osode will still cost you a lot of money, but not as much as Ranger will. However its gear is much more heavily dependant upon a few R/E pieces like Byakko Pants to be even semi-decent, and these usually have a queue. Unless these sort of pieces are available to you through your LS, this isn't necessarily a good choice. Always popular in a merit party and can swap out to polearms for birds (GO GO Penta spam!).
Puppetmaster - Has some amazing niche uses like hateless nuking, but is unfortunately way too limited in its roles end-game, and on that basis, this is not a job for you if you want one which is "highly usable in endgame".
Corsair - Has a lot of uses end-game, but it still a support role and is played as such. You will never be short of a merit party with it, and has the fun side of being able to chuck out a ranged WS every now and then. Based on the fact you already have two mage jobs, this is only a half-step away from the mage role (in most of the circumstances you will be using it end-game) and you may find it boring. There are a million COR's who will now scream they can DD, but it will never be a solid DD in the way a WAR / SAM / MNK / DRK will.
In summary, if you are able to obtain money easier than R/E items, go for RNG. If you have reasonably easy access to the important R/E pieces choose SAM. It doesn't matter what anyone tells you, spamming WS's is good fun. If you want to be "highly usable" end-game, forget PUP. And if you don't want to go full DD, want something quick to level, or like to merit, go COR.
If it were me, I would pick SAM. It meets all of the criteria you have asked for, but then I may be biased as I'm already 75 SAM...