Does this mean good research is completely subjective?

No.

This is a crucial distinction.

It would be wrong to say:

“Scholars decide what is good, therefore anything they call good is good.”

Academic standards are socially developed, but that does not mean they are arbitrary.

For example:

Accurate quotation of a primary source

can be objectively better than:

Inventing a quotation.

Similarly:

A statistical conclusion based on an inappropriate sample

can objectively have methodological problems even if a prestigious scholar produced it.

So there are two different questions:

Question 1: Are standards socially constructed?

Often, yes.

Question 2: Does social construction mean there are no objective standards of quality?

No.

A standard can be socially developed while still being rationally defensible and evidence-sensitive.