Yes tool chain is what set apart the licencable engines to the inhouse build engines in the pro studio league. But it is also the support part that crusial. For large production with army of artist. The productivity effeciency is key.

The key here is also the production of a full big game.

But my guess is that not relevant for a hobby game engine starter. Who get it first shot at first engine. For learning purpouse.

But for a engine builder you don't need a full game. Just a demo sized game which incorporates all the features a full game needs.

Then when the small team or lone dev want assets. Our lots of it. There is this alternative way of going PCG way. In pure form the high need for a artist might even disapear. Maybe just one is enough might be luxory. A team where there are more programmers then artist.

A example is crowed funded Star Citezen with big funds doing conventional production also starting multi big studio. Need a productive tool chain which are offered by full licencable engines with source and support. Crytech engine.
Compared to infinity a more pure PCG single dev project relying on PCG procedural content generation.