Yeah, you definitely could do that; would be more resource consuming for sure, but it's absolutely feasible, and makes sense if the benefit outweighs the cost. Apps are generally a mix of non-blockchain and blockchain code, with the actions a user can take, such as uploading a video/making a post/uploading test results usually often being stored in a local database, AS WELL as the blockchain, with the blockchain usually acting as the permanent, reliable record, but the local DB being utilized for speed and efficiency.