I have a big list of landing pages on a spreadsheet. My goal is to get these landing pages' traffic data from Google Analytics within the last 9 months to my spreadsheet.
Is it possible to implement this with formulas?
You have to use Google Analytics API, luckily there is an add-on that does the job for you:
https://developers.google.com/analytics/solutions/google-analytics-spreadsheet-add-on
The Google Analytics Spreadsheet add-on makes it easier for Google Analytics users to access, visualize, share, and manipulate their data in Google Spreadsheets.
Here you can find similar tool, GA360 Unsampled Spreadsheet Add-on, if you need to export Unsampled report in Spreadsheet from Google Analytics 360:
https://www.analyticstraps.com/google-analytics-unsampled-reports-spreadsheet-add-on/