Diastatic power should not affect alcohol content, if it's enough. If iodine test came out negative, and there is no unconverted starch, you got all the sugars that was possible. Only if diastatic power was too low to fully convert, final amount of simple sugars will be lower. But that would mean starch in your brew, a bad thing on it's own.
Mash regime should have bigger effect. At 62 C you will get almost exclusively fermentable sugars. At 72 C you will get as much unfermentables as possible.
Yeast "potency" you mentioned is actually called attenuation level, or apparent attenuation. You are right, it changes final alcohol content of your brew. The higher it is, more alcohol and less body you will get.