There are 3 separate statements you could make. SweetHome 3D IS slower than competitive projects written in C++. C++ tools tend to be faster than comparative

There are 3 separate statements you could make. SweetHome 3D IS slower than competitive projects written in C++. C++ tools tend to be faster than comparative Java tools because of fast startup time, no GC, and being the default choice for performance sensitive projects for decades. C++ is definitively faster because of inherent advantages. You appear to be jumping to the third based on the first which appears erroneous in argument even if you turned out to be correct. In actuality it appears that for most things in the same ballpark language choice isn't necessarily the only or even the most important factor. This is even more true for things where startup time is an inconsequential factor, with better GC that doesn't result in lengthy pauses, and where development time is a substantial limiting factor wherein being quicker to work with may result in more time available to improve other design choices yielding as good or better results.