Disagree. Unity is pretty strong on mobile and multi-plattform. Enough to survive on this alone (imo). I also think Blueprints is already a strong competitor for the share of users who find C++ too complicated (non-programers and people who have only dabbled in scripting). I think for "traditional programers" the difference between C++ and C# isn't big enough to make a difference and frankly people with a gamedev background probably prefer C++.

That being said as a non mobile guy who occasionally dabbles in engine stuff I'll be migrating to Unreal for good now. I haven't been a paying customer for a while now but I used to pay for Unity back in the super early days of AR.

Or I guess take another serious look at Godot :D