I was of the same mindset for a long time; SmartThings, Hue and Google Home all worked well enough together to do what I wanted. But holy shit, Home Assistant is on another level and I only wish I’d installed it sooner.
The only real downside is that it makes home automation somewhat addictive and, by extension, expensive. I spend quite a lot of my time thinking about how to automate more of the things, and have a never ending list of stuff that I want to add to my setup.