Oh yeah, if you want something reflecting objective reality, sure absolutely. You need context out the wazoo. But, if you're just measuring a spread of bias from Democrat to Republican among the hegemonic media sources that are already only reporting within that context you can probably be pretty accurate for which way they're leaning. Especially since within that spread "reporting" is largely gonna be providing support for talking points from one party or the other.
Oh yeah, if you want something reflecting objective reality, sure absolutely. You need context out the wazoo. But, if you're just measuring a spread of bias from Democrat to Republican among the hegemonic media sources that are already only reporting within that context you can probably be pretty accurate for which way they're leaning. Especially since within that spread "reporting" is largely gonna be providing support for talking points from one party or the other.