Guillermo Söhnlein is pushing back on the "Titanic" director's assertion the submersible was "too experimental to carry passengers" ... saying it's impossible for James to know all the details.

Guillermo went on Times Radio Friday in the U.K., and defended OceanGate and Stockton, saying ... "It's impossible for anyone to really speculate from the outside ... I know from firsthand experience that we were extremely committed to safety and risk mitigation was a key part of the company culture."

Remember, James is blaming the tragedy on Stockton -- who was piloting Titan when it imploded -- claiming he ignored warnings from the industry about the safety of Titan's design, and then made matters worse by taking tourists aboard the vessel.

James, who made 33 dives to the famous shipwreck, said he and others in the submersible community voiced concerns about the Titan submersible, but Stockton pushed forward, undeterred -- kind of like the Titanic captain who went full steam ahead into an ice field.

Guillermo says James' views are not gospel -- he says there are differing opinions and views within the industry about every aspect of deep ocean dives and submersibles ... and, most importantly, he says James wasn't involved in the design, engineering, building, testing or diving on Titan.

Despite the 5 deaths aboard Titan, Guillermo says this isn't the end of OceanGate ... he says the company needs to investigate what went wrong, and apply those lessons moving forward.