Dash seems a poor substitute. A dash is closer to a period. Semicolons work well for when just using multiple commas would become ambiguous. Shorter sentences also solve that, but sometimes you want a run on sentence, sometimes you want to splice more context in at this very point. & sometimes you just want to drop a conjunction
Writing has no laws, only rules meant to be broken
English is also a descriptivist language, rather than prescriptivist. ie English has no spec, unlike French (tho you then have French as it is spoken & French as it is specified). As much as Oxford might want to reign it in, they are only cataloging what the collective spews
Using "&" in place of the word "and" does depart from common usage (though there's no "law") and does so in such an overt way that it appears pretentious.
> Semicolons are hot
Dash seems a poor substitute. A dash is closer to a period. Semicolons work well for when just using multiple commas would become ambiguous. Shorter sentences also solve that, but sometimes you want a run on sentence, sometimes you want to splice more context in at this very point. & sometimes you just want to drop a conjunction