Girlfriend has a 2014. Headlamps are one of the dual-filament types - not what I would prefer.
While I can see where you're coming from, to a certain extent, it's not necessarily true that composite headlamps using a single compartment for a high/low beam are
always better than those that use separate compartments for the high/low functions, at least from a photometric standpoint. It is true that there are some compromises involved in a single-compartment high/low headlamps-- but good headlamps are good, and bad headlamps are bad. Practically speaking, it's
easier to make a good dual-compartment high/low lamp. It still doesn't mean that
every dual-compartment lamp is better.
They need to be properly aimed
True of all headlamps.
and would likely benefit from better bulbs such as Philips Extreme Vision.
Photometrically speaking, any lamp benefits from better bulbs when those better bulbs exist.
Short of ridiculous voltage drop at the bulbs I wouldn't mess with a relay harness.
And it could just be that a huge voltage drop is accidental, not the result of poor design. It may just be that there's a bad ground or feed somewhere that is easily correctible, and not necessarily requiring a relay kit.