Why Port Arthur did not make Russian defenses unbeatable

If Port Arthur showed how much modern defenses favored the defender, how could the Allies hope to force the Dardanelles?

Strong defenses raised the cost but did not decide the campaign; Japan's victory at Port Arthur showed how Russian logistical weakness could outweigh fortifications.

The question treats Port Arthur as evidence that modern fortifications had shifted the balance decisively toward defenders. Logistics were a central reason Japan could defeat Russia in the Russo-Japanese War. Russia's immense distances and inadequate infrastructure made it difficult to reinforce and supply a remote theater, a problem not erased even by the Trans-Siberian Railway. The analogy applies to Gallipoli: fixed defenses increase the cost of attack, but they do not decide a campaign independently of transport, timing, and concentration.