I think the "largest" volcano title is something that media people use for click bait, using whatever definition can be made to fit the volcano they are writing about at the moment.
In the case of Mauna Loa, I think that it is the biggest in volume when measured from its base to its summit, if you assume that its base is the bottom of the Pacific Ocean and the whole island is the volcano. The tallest is its neighbor, Mauna Kea.
And the term "active" is also poorly defined and abused by writers looking for superlatives. For instance, "active" sometimes means "actively erupting", sometimes means "is still expected to erupt again in the future" and even "might be able to erupt again some time in the distant future".
Smithsonian Global Volcanism Program defines "largest" by volume measured from base to top, even if the base is underwater.
"Active" is defined as having erupted in the last 10,000 years or is showing signs of unrest.
"Dormant" volcanoes erupted longer ago than 10,000 years but scientists believe they are still connected to a magma chamber.
"Extinct" volcanoes are no longer connected to a magma chamber.
Geologists classify volcanoes into three distinct groups: dormant, extinct and active volcanoes. Dormant volcanoes haven’t erupted in a long time, but they could again; extinct volcanoes have erupted for thousands of years and might be dead. Active volcanoes, on the other hand, erupted recently...