I seriously don't get it. The highest possible health a toon can presently have at 25% is 4,710 (Nightsister initiate). But that's an outlier. More common are numbers like 3,948 (Kylo Ren), 3,379 (Poe Dameron), 3,244 (old Daka), 2,894 (Luminara) and 2,734 (Dooku).
Savage's special ability is basically a non evadable attack in the ~4K region. Except that often it doesn't activate until a toon is brought to significantly lower HP than that. 25% is the threshold. It's highly likely that any attack that brings a toon below 25% actually brings it down to 15%, maybe even just 10%.
At that point, Savage's special is more or less pointless and indistinguishable from his regular attack. Especially with dodging playing such a small part in the game presently.
Savage could be great vs PvE bosses though. That's about the only use I can find for him.