Sorry, I wasn't differentiating between pardons and commutations because wikipedia didn't for any other President than Obama. So I went to the DOJ website for a breakdown. You are correct that Obama pardoned fewer than those Presidents. His commutations however are significantly higher.
Eisenhower pardons- 1110, commutations-47, Total- 1157
Nixon pardons-863, commutations-60, Total- 923
Ford pardons-382, commutations-22, Total- 404
Reagan pardons-393, commutations- 13, Total- 406
Obama pardons-212, commutations-1715, Total- 1927
I think this gives a better comparison than strictly using the term pardon.
Since, you've read further into this, did you happen to come across the reasoning for these commutations? And you're clear, on what a commutation does, right?