Rubinstein did not invent 3...dxe4. The first Rubinstein game with 3...dxe4 (1903) saw him playing White ...
Before Rubinstein played it, Bird, Delmar and Blackburne played it amongst others. Another example is Steinitz-Lasker, WCh m 1894, 8th game.
Nimzovitsj did not invent the 3.e5. Greco, Staunton and especially Louis Paulsen preceded.
Finally Nimzo was certainly not the first to play 3...Bb4. Just two examples are Esser-Marshall, Amsterdam 1911 and Réti-Euwe, Amsterdam 1920.
Both Rubinstein and Nimzo played the French less often than Alekhine and Spielmann. They being important players of the French defense is just an urban chess legend.
Spielmann is on my list, because he was the first to decide a tournament with the French: Semmering 1926. Moreover he was the first to play 1.e4 e6 2.d4 d5 3.Nc3 Nf6 4.Bg5 Bb4 5.e5 h6 6.Be3 on a regular base- a rather topical line these days.
Finally I simply always prefer Spielmann above Nimzo and Rubinstein.
If it were a poll on say the QGD, Spielmann also be on my top 5