Depends on what speed you want to hit. Assuming Hydreigon's max speed of 324, Latios would be running a spread of Timid 100 HP / 252 SpA / 156 Speed. The following would be the results:Yea. hydreigon > latios
i have a question.
if they were made so that they have the same speed, who would have more bulk and power?
Latios: 326 / 194 / 196 / 359 / 256 / 324
Hydreigon: 326 / 221 / 216 / 349 / 216 / 324
Latios boasts higher SpA and SpD while Hydreigon has greater physical bulk (and attack, but that is somewhat irrelevant).
Between neutral Hydreigon's max speed of 295 and 319, Latios is significantly stronger (it can run Modest and still be faster), but is less bulky because the EVs are poured exclusively into SpA and Spe.
At 295 Spe and lower, Hydreigon is again marginally weaker but has higher physical defense.
Honestly, though, Latios' ability to outspeed the 100-110 group is the reason to use it in the first place. Manipulating its nature/EVs to mirror Hydreigon is misleading, as the marginally higher SpA is offset by Hydreigon's access to Fire Blast, Focus Blast, and Dark Pulse.