I can see two reasons why Eisenhower is underrated. First, he was a Republican; we both know how liberals try to control the historical narrative these days. Second, as a general he learned to delegate authority, and as president he did it well enough that at times it looked like he wasn’t doing anything at all, except playing golf on the White House lawn.
Once I heard some joker say that FDR proved you can be president for life, Truman proved anyone can become president, and Eisenhower proved you don’t really need a president. Apparently that person didn’t know that in the Eisenhower administration, the action was happening behind the scenes.