flask is a micro framework and therefore i understand its limitations compared to other options, but it is still good for small projects. i dont agree that flask is a weak or poor framework and your reasoning sounds like it is more of your preference than fact. django is more robust than flask, but also has a larger learning curve and would require just as much coding if not more than flask.
i also understand that php could be a good option as well. however, you have to download and install multiple applications, such as apache and xampp to complete this project. it is not a lot, but it can be difficult to get past for beginners.
as with any project, we have many options when it comes to what we can use, and what we use is dependant on our preference and comfort level. you obviously have a preference for php and im sure others have their own preferences. it doesnt mean other options aren’t good.