Just thought I'd throw in my two cents.
First of all, it's true that Mithra have massively higher dexterity that all the other races. At 70, they'll have 10 more than anyone else. However, I agree that it's pretty much a myth that race matters at all. When I lvled my War up to 30, I was partying in Batilla Downs with a half Japanese team. We had a Taru Paladin, who was a fantastic tank - I never needed to voke a mob off him or our mages, and it was easily one of my top-ten parties of all time.
Currently my Sam is sitting at fifteen, having suffered through a craptastic party in the Valkrum Dunes today where I was expected to tank. As a Sam/War I can tank well, but ONLY (I repeat) ONLY if we have a proficient whitemage. The whitemage was not proficient, or at least he suffered from terrible lag.
Though Sams were originally expected to be damage dealers, they were also DESIGNED as backup tanks. The requisite sub for Sam IS War (this is proven by the fact that advanced Samurai gear has plusses for Warrior traits like double attack, while Ranger gear has plusses for Ninja abilities) - tanking is something we're expected to do. The higher up in lvl you go, the more you'll discover you need to do the job expected of you, or you won't get into parties, and that equals no lvls. "Pffft - screw parties then," you may say, "I'll just solo."
And you'd be very smart, if it was possible to solo Easy Preys at much higher lvls - but it's not. Partying is 100% necessary in FFXI, and it's necessary for a Sam to have Voke.
Moving back to the racial issue:
As an Elvaan Samurai with the worst dexterity in the game, I've never had a big problem hitting even ITs. At 14 I put on the +2 Dex balance rings, and now I can rely on every strike for its tp.
Anyway - back to my craptastic Dunes party:
In the group was a Redmage (very proficient, but I've seen rdms use their weaponskills and this one didn't - the Drk didn't either - no skillchains for me) who was constantly using Enthunder. That got me thinking, just as you, that perhaps the weapon enhancements of a redmage would make a good compliment for Samurai.
It's all well and good to take any job you want - be a Sam/Brd if you want, just for the latent party hp/mp gains. It's totally up to you. BUT:
The compliments of subjob to main jobs in FFXI is designed to work in 2 ways: 1) to make up for the weaknesses of your main or 2) to enhance the strength of your main. This is why most Wars sub Monk to get to 30 (Strength Dex and Hp boost) - why a Whitemage will sub Summoner (massive Mp boost and mp gain abilities). You'll occasionally see a Sam/Thf, and you know that was to make the Sam a more effective damage dealer. More dex, Sneak & Trick attack, et cetera.
Subbing rdm with Samurai does not make up for a Sam's weaknesses, nor does it compliment its strengths well.
I myself am tempted to put War aside and use Thief as my Sam's sub, but I won't. When I'm in a party and the mob goes for our mage, I want to voke it off. I want to do the best I can to advance my party, and myself.
That's just my two cents. Hm - maybe it was more like a quarter.
15 Sam / War 7
Chances 45 Alliance Rogue guild : Can't PvP
"Kill schmill - think of it as pest control"