The Big Picture
In the past, developing line-of-business apps with SharePoint was largely split into two camps: systems bolted together by power users using a tools like SharePoint Designer or InfoPath and systems built by developers using full development tooling like Visual Studio.
If you’ve been involved with those projects long-term, you may well have become jaded with those as a viable option.
I urge you to take another look.
SharePoint as a development platform has metamorphosed immeasurably over the last couple of years, to become truly enterprise class.
Modern SharePoint Online development consists of front-ends and full customisations built with SharePoint Framework (or SPFx). Current best practice is to build serverless back-ends using services from Microsoft Azure, such as Function Apps, Logic Apps with many, many database options.
Also, advanced users and developers alike can use Microsoft PowerApps and Flow to build business apps, in a structured and manageable way. (http://1jj.uk/clouddev)