I am currently using the below code to import 6,000 csv files (with headers) and export them into a single csv file (with a single header row).
#import csv f
Are you required to do this in Python? If you are open to doing this entirely in shell, all you'd need to do is first cat the header row from a randomly selected input .csv file into merged.csv before running your one-liner:
cat a-randomly-selected-csv-file.csv | head -n1 > merged.csv
for f in *.csv; do cat "`pwd`/$f" | tail -n +2 >> merged.csv; done