True arbitrage is competed away in microseconds. If you can see one, you are almost certainly missing something - transaction costs, execution risk on one leg, funding, settlement mismatch, or a borrow constraint.
The interview question is always "A and B are identical but priced differently - what do you do?" The naive answer trades it. The good answer asks why they differ and enumerates the frictions first.
Relative value is what most strategies actually do: betting on a statistical relationship reverting, with residual risk. Sizing that like arbitrage has caused repeated blow-ups.