Unity has 2D platformer support built right in, and the tricky bits -- like the time mechanic -- could be written as an extension. Heck, there's probably a time rewind mechanic in the Unity Asset Store as we speak. They've so far advanced that you're just never going to keep up writing a bespoke engine because they've benefited from being integral to the industry as a whole. Furthermore, the skills you develop on your own with your little bespoke engine aren't going to translate into the industry, where everybody uses Unity or Unreal.

It's kind of like how you're never going to build a graphic design business using GIMP, Krita, or Inkscape. They're all nice tools for amateurs and dilettantes, but entire industry standards and processes have coalesced around Photoshop and Illustrator, so that's what you use. The open-source alternatives are decades behind the curve here and in some ways, will never ever catch up. Good luck getting PANTONE support, which is critical to graphic design for print, into GIMP or Inkscape, for instance.