This looks sleek and well-made! However, this is a pretty crowded space. Spreadsheet Converter (https://www.spreadsheetconverter.com) and Spreadsheet Web (https://www.spreadsheetweb.com) are directly comparable and have been around for years. (Like Publisheet, Spreadsheet Converter offers an Excel add-in.)
Then there are lots of web app builders, including Calculoid (https://www.calculoid.com), Calconic (https://www.calconic.com), uCalc Pro (https://ucalc.pro) and Calcapp (https://www.calcapp.net/lp/website-calculators/), that require more work to get from an Excel sheet to a web app, but get the job done with an end result that doesn't look like a spreadsheet. How does Publisheet improve on the competition?
(Full disclosure: I'm a co-founder of Calcapp.)