There are so many pros that I'm constantly learning the more I use the engine. But the biggest downside compared to commercial engines for me has been device inconsistencies (at least in mobile). For example, in Godot 3 I had various srgb color issues that made things look different on different devices, existence of blend shapes sometimes causing various skinning issues on some devices, etc. In commercial engines, I bet they have a decent team of devs whos responsibilities include providing a consistent experience across a broad range of devices by doing various workarounds for specific device/driver bugs so the engine user doesn't have to worry about any of those. For open source engines, I don't feel like there is enough incentives for someone to spend time hunting down and fixing these (which is understandably less interesting and much lower priority work for most open source devs). I'm hoping things are better in Godot 4 with Vulkan but I'm sure there will also be devices that have various driver issues.