The world is not binary, nor black & white. There is an entire spectrum of solutions between a spreadsheet and a highly-structured app. Sure, you can use a spreadsheet for anything, it's quick, and provides nearly no structure. You can also use a specialized application, tailored for the particular processes at hand, that does error checking on input, validates data integrity, and does not let you break data structures. And there is a whole spectrum in between.
One thing to note is that a spreadsheet (OPs insistence on calling it "Google Sheet" is amusing after years of hearing people call it "excel", it's a spreadsheet, people!) is a poor-man's relational database, with most spreadsheets having a single table, or multiple tables but modeling no relations. And you can't model relations in a spreadsheet in any meaningful way (imposing constraints, checking integrity, etc).
Written from the perspective of someone who makes a living providing a SaaS for (among others) inventory control, for which a spreadsheet is a direct competitor. Also, from the perspective of someone who has seen a lot of customer spreadsheets with inventory, not one of them in any way correct or containing good data.
One thing to note is that a spreadsheet (OPs insistence on calling it "Google Sheet" is amusing after years of hearing people call it "excel", it's a spreadsheet, people!) is a poor-man's relational database, with most spreadsheets having a single table, or multiple tables but modeling no relations. And you can't model relations in a spreadsheet in any meaningful way (imposing constraints, checking integrity, etc).
Written from the perspective of someone who makes a living providing a SaaS for (among others) inventory control, for which a spreadsheet is a direct competitor. Also, from the perspective of someone who has seen a lot of customer spreadsheets with inventory, not one of them in any way correct or containing good data.