A druid with the special ability wild shape who takes the feat Shaping Focus increases his effective druid level by up to 4 for the special ability wild shape but not beyond the creature's total character level
Thus a typical Drd4/Ftr3 who takes the feat Shaping Focus employs the special ability wild shape a if the Drd4/Ftr3 were a Drd7. (I chose the Drd4/Ftr3 instead of Drd4/Ftr4 because in typical campaigns the latter character wouldn't have a feat available at that precise total character level.)
However, the feat Shaping Focus doesn't and, in fact, can't help the saurian shaman Drd4/Ftr3 who, because of his archetype, lacks completely the special ability wild shape until he reaches level 6 as a druid:
At 6th level, a saurian shaman’s wild shape ability functions at her druid level –2. If she takes on the form of a reptile or a dinosaur, she instead uses her druid level +2.
The saurian shaman Drd4/Ftr3 just doesn't have the special ability wild shape, therefore he's unable to meet the prerequisites of the feat Shaping Focus and wouldn't receive the feat's benefits were he somehow able to, until he's at least a saurian shaman Drd6.
Likewise a creature with no druid levels that somehow managed to take the feat doesn't gain the special ability wild shape as if the creature were a level 4 druid.
By analogy, the feat is like a coupon for extra 4 toppings on a pizza; one must still buy a pizza to get the extra toppings.