Unity’s product is very good and competitive. It’s easy to customize for your own needs, but only up to a certain point because the source codes are not freely available. You could get them for money, but it’s not recommended. With UE4, on the other hand, all source code is freely available and modifiable. You could fix engine bugs yourself and send the fixes to Epic on GitHub. This is what I missed most in Unity.
In the last 5 years, Unity has caught up a lot with UE4 in terms of graphics engine and performance. In places, it has even surpassed it. The editor and tools’ performance is significantly better, which speeds up work tremendously. In UE4, I spent several hours a day just compiling code. I don’t see anything wrong with the product, and it competes equally with its rivals. I haven’t tested UE5, but it seems to have taken a really big leap forward.
I don’t want to talk too much about my own game engines to maintain some level of anonymity, but I’ve worked on in-house 3D game engines for PC and mobile.
In summary, regarding the investment case: Unity’s success will not be due to the product itself.
Edit: @Kesa86 I have no experience with the Unity service part.