I think their C++ library is one of the reasons they can create capable software so quickly actually. They have jetisoned just a tonne of C++ nonesense and added some really nice modern features such as how they handle memory and errors.
Also, you would think that having to implement EVERYTHING themselves ( they are making their own image decoders as an example -- inclding SVG ) would slow them down. However, as it is written in a mono-repo from soup to nuts, this allows them to very rapidly add support throughout the stack. They do not have any of the endless conversation and arguing that happens between components in Open Source. They do not have to work around things missing upstream. If they need something, they add it.
Also, you would think that having to implement EVERYTHING themselves ( they are making their own image decoders as an example -- inclding SVG ) would slow them down. However, as it is written in a mono-repo from soup to nuts, this allows them to very rapidly add support throughout the stack. They do not have any of the endless conversation and arguing that happens between components in Open Source. They do not have to work around things missing upstream. If they need something, they add it.