You're quite right; Altman is the starting point, and before Altman others swung back and forth among scenes and situations too. But with young directors Altman is now an influence through Anderson. Magnolia is more of a focal point than Altman. Because in Anderson the method is used with the eye of a new generation.

Gabriele Muccino's The Last Kiss/L'ultimo bacio has frequently been said to have a heavy debt to Magnolia. Indulging in some wordplay one Italian wrote, "Muccino cucina una magnolia all'amatriciana." No doubt about it, Magnolia is a big influence now, and since Anderson is arguably even more self-indulgent than Altman, the influence can't always be for the best.