I think there are already tags for complexity-theory and time-complexity. The descriptions are similar. What benefit does runtime-analysis bring to the table?
Time complexity is about asymptotic bounds on worst, best or average case resource consumption needed to solve problems.
Runtime analysis deals with explicit runtimes of a given algorithm on specific inputs (and functions thereof).
Asymptic best/worst/average case behaviour of a given algorithm falls somewhere in between.
Algorithm analysis is way broader than runtime analysis, as it also subsumes space and energy consumption, parallelity, correctness and every other property an algorithm can have.
As we have not used runtime-analysis a lot I guess we can drop it in favor of algorithm-analysis; most will want to analyse runtimes, anyway, so we might need tags to mark other measures but certainly not runtime.