The Whale v. Elephant series is not over.
A reductionist reading of any text is generally unfruitful.
Mahan's theories of naval power were hardly "eclipsed" by German and Russian Army strategists.
It is not a question or reductionist readings any more than one of extrapolative reading.
Not being familiar with the full content of Mahan's works I could only find a bibliography of his texts (are any still in print?), but to judge by the titles it appears that he was an engineer who applied civil engineering to fortifications.
The history of warfare is one of static forces in fixed positions surrounded and overwhelmed by more mobile forces as demonstrated in the 20th century by (a) Western Front WWI 1918, (b) France 1940, Soviet Union 1942, (c) British North Africa 1941/42, (d) Germany Eastern Front 1944/45 (e) 1st & 2nd Gulf Wars.
Thus, Mahan's works on entrenchments and fortifications are interesting for light they might shed on defensive patterns of enemy positions, but ultimately they were redundant by the end of the 19th century (cf., the US Civil War vs the 2nd South African (Boer) War).
Where mobile forces clash it is the more aggile (and securely supplied) that wins. Fortifications will slow an enemy but unless you are capable of striking back at them (Battles of Kursk, El Alamein, etc), fortifications are a trap.