I think that's a bit misleading: Smokeless powder was introduced in 1886, but only for rifles, it would take nearly 10 years before the technology could be safely adapted to large bore artillery. The gun could be considered an effective piece until 1900. That it was a ML was the more obsolete technology, but the sophisticated loading system compensated for that. That it was an ML was due to the question of Metallurgy in something of that bore size!
That the writing on the wall was clear by the late 1880s, but only as a technical excercise, practical applications always lag behind.