RISC lost to x86 in the PC and server space even when RISC was distinctly faster. The only RISCs periodically faster than x86 over the last decade are IBM's Power chips and those have far higher power budgets, chip level bandwdith, and cost structure.
For ARM to break into the PC and server space today it will face the same software issues that PowerPC/MIPS/Alpha faced in their day but with the second disadvantage of being way back in performance instead of faster or at par. ARM's advantages over x86 are business model based (cost/flexibility for OEMs rolling their own unique SoCs). IMO ARM's supposed power advantage is far overblown.