It's all about USABLE power and smoothness. No add-on system will ever reach the completeness of a system designed to work as a whole from a single serious manufacturer.
They have control over every motor aspect and their close bicycle manufacturers work on frame geometry, weight distribution, etc. So the eBike experience is a total system, not just a bolt-on afterthought.
Cheaper is one thing, quality as a system is another. This is a rule I follow on almost every option I have in my life. Go with the better one if you can. More quality, more enjoyment, more long time support.
Its a different thing if you have unlimited time and love to tinker with your tools. A bolt-on system can be a nice winter project. But for MTB (and even more full-suspension) use, Bosch, Shimano, Yamaha (alphabetical order) would always be my top options.
@zoumerela where do you live? There is a nice Cube dealer in my area who is a crazy eMTB rider himself too. He organizes some demo rides some points (at least before the Covid era