> A switch to proportional voting could require constitutional changes in most places.
Less places than you might think. It especially wouldn't for Congress (so long as it was proportional by a method similar to STV within state delegations, or within some subset of state delegations), as the only barrier there is a statutory prohibition on at-large districts for delegations greater than 1, adopted to head off the use of FPTP at-large districts to systematically deny representation not minorities.
> Also, proportional voting introduces all kinds of unnecessary problems like not having districts
Party list proportional would do that, but most other proportional systems would not.
> and thereby constituents having their votes diluted
Proportionality doesn't dilute votes; the more proportional a system is the more efficiently it allocated votes to give them maximum effect.
> and not having a specific representative
Proportional systems don't need to have that effect, either, no matter how you measure it (and FPTP—and any other simple singlr-member district system—definitely has that effect for supporters of the nonwinning party in a district, who are effectively unrepresented entirely.)