Here's the tl;dr version: Sunbreakers are getting weaker; Strikers are getting stronger; Defenders are getting some help.
Senior design lead Sage Merrill presented a bunch of data on the Crucible performance of Titan subclasses versus other classes, including graphs, to explain Bungie's upcoming tweaks to Titans. Merrill said that Destiny: The Taken King was meant to give Titans "their moment in the sun," but said the studio "may have overdone [Sunbreakers] just a little bit."
Over the past three months, Sunbreaker Titans have had a much higher average kill/death ratio than Strikers (lower than intended) and Defenders (intentionally low, because they're a support class), and Merrill said that "can be attributed mostly to the Hammer of Sol." Therefore, Bungie wants to give other players a fighting chance against Sunbreakers in the Crucible, underscore the Striker's role as a melee-focused subclass and make Defenders more viable in their support role.
All Titans are receiving a 12.5 percent boost to their melee range with the 2.1 update. Defenders will once again recharge their grenade and melee when they cast Ward of Dawn. The Striker's Storm Fist will deal 18.2 percent more damage, while the Unstoppable passive ability will offer 25 percent more damage resistance. The Sunbreaker's Hammer of Sol will provide 9.09 percent less damage resistance while it's active. The hammer tracking from the super's Flameseeker passive ability will drop by 25 percent and the Forgemaster splash damage radius multiplier from hammer detonation will drop by 20 percent.
You can see the rest of the changes in Bungie's blog post.
"Looking at these changes the first time, some may say we ruined the Solar Titan," said Merrill. "I assure you we have not. They are still very, very good, but you'll find that out for yourself soon enough."
Update 2.1 will deliver a fresh round of weapon balance tweaks, new uses for Etheric Light and Wormspore, and a sizable expansion to the game's array of exotic gear. For more on The Taken King, read our review.