I mean yes no kinda Konqueror simply accepted a bunch of downstream patches, including a name change.

...more or less. It could for a long time use all three of KHTML, WebKit (fork of KHTML) and QtWebEngine (Blink wrapped for Qt, that is, a fork of WebKit), they recently removed KHTML support because noone was updating it and it hadn't been the default for ages.

If they hadn't implemented multi-engine support in the past they probably would've switched over to "whatever Qt provides" right-out, it's KDE after all. Ultimately they're providing a desktop, not a web browser. Back in the days they did decide to roll their own instead of going with Firefox but it was never a "throw project resources at it" kind of situation, there were simply KDE people who felt like working on it. Web standards were a lot less involved back around the turn of the millennium, and also new and shiny. Back in the days people thought that HTML 4.01 Strict and XHMTL would be a thing that servers actually would start to output instead of the usual tagsoup.

If you're that kind of person right now I'll point you in the direction of Servo. No, Firefox doesn't use it and it's not a Mozilla project any more, Firefox only included (AFAIK) parallel CSS handling, the rest is still old Gecko.