The 10,000 Malistaire is way too easy for people 58+, now that we have critical and the new spells. PLEASE bring the 100,000 Malistaire for legendaries. (but keep the 10,000 if you're soloing) Some people actually want to farm him and have fun :-(
You don't know if the 100k Malistaire would be easy for 58+. If I recall correctly, everyturn he casted Meteorite that did extreme damage. It took some serious tactics to beat him for the 6 people that did, albeit it would be easier at 58+.