Consider that the Brittanic only sunk due to a mine, and the crew acted bravely and efficiently to evacuate nearly all lives. 30 died, but that was due to lifeboats that were accidentally deployed without the Captain's consent while he still had the engines running--they were pulled into the port side propeller, which was already partly above the water line due to the ship's bow tilting forward. When he realized what was happening, orders were given to stop the engines.
The captain was attempting to steer the ship to a nearby island in hopes of beaching the vessel so that it might be salvaged, but the rudder sustained damage and wouldn't function. In a last ditch attempt, he cut the power to the starboard propeller in hopes that the port and center propellers would steer the ship to the island. It might have worked, but the catch 22 here was that the forward propulsion caused water to flood more rapidly into the damaged hull--they simply couldn't make it to the beach at the rate she was sinking. After one final attempt at turning the engines back on and heading for the island, the captain cut the engines a final time and decided to continue evacuating everyone. It was very close, with the final crew members left on the bridge only jumping out once everyone else had evacuated and the water was already beginning to creep onto the bridge deck. This ship sank in about half the time it took Titanic to go down, so it is pretty remarkable they got everyone out before the final plunge.
Had Brittanic, given her improved designs, hit the same iceberg and at the same angle as her ill fated sister ship, she most likely would have survived at least until the Carpathia arrived on the scene--it is likely she would've stayed above the waterline but with a severe list. She may have even been able to limp back to port for repairs. The Brittanic also had some motorized lifeboats. Had the Titanic had one of these, they could have motored to the nearby California to request assistance (the California crew saw the lights of the Titanic but were unaware of the situation due to having shut their radio off for the night. They almost certainly could have made it to the Titanic in time had they known).
Given all of that, I consider the Brittanic a success compared to Titanic. If not for the mine she hit, she probably would've stayed in service for decades like her sister Olympic. Olympic herself might've stayed in service even longer, but by the mid-thirties, the world was in an economic crisis. It was more feasible to scrap her. If she'd not been scrapped, she might be a museum ship today.
I actually find the story of the Brittanic more fascinating and exciting, but I can see why it's less known, as it wasn't a disaster on the same level as Titanic, thus failing to fuel as much of the morbid curiosity that tends to linger over disasters like Titanic and Hindenburg.
Here is a real-time animation of the Brittanic's final plunge. Although she didn't split in half like her sister, they otherwise went down in a very similar manner, although Brittanic in considerably more shallow waters. The final 15-20 minutes or so of either ship's sinking must have been terrifying, as it suddenly became more rapid. The hours prior as either ship sank more slowly must have lulled some crew and passengers into a false sense of security.