there are dozens and dozens of grades of "stainless steel". Some grades (the 300-series is typical) have very high corrosion resistance but lower strength and hardness and cannot be heatreated to improve their strength. Other grades (400-series) have lower corrosion resistance but can be heat treated to very high strength and hardness.

The 300 stainless steels are primarily used for chemical equipment and piping fabrication and 304 is used for most stainless steel spokes. The 400's include the so-called tool steels or cutlery steels and can be used where strength is a major consideration and corrosion resistance is not as important since the environment they are typically used in is not as demanding.

Similarly there are many grades of titanium. CP (chemically pure) Ti is extremely corrosion resistant but has modest strength and only fair fatigue life. It's main use is in chemical equipment manufacture.

Alloy Ti's like 3Al/2.5V (3% aluminum, 2.5% vanadium, balance Ti) or 6Al/4V are much stronger and have great fatigue life but are more difficult to machine and shape. 3Al/2.5V is the Ti alloy most commonly used in bike frame manufacture. A few frames have been made from the stronger 6Al/4V Ti but the consensus seem to be that its extra strength doesn't make up for the difficulty in fabricating it.