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If I'm understanding you correctly, you touch on the point that I (probably badly) tried to make - by slowly cooling it during heat treatment, you can post-weld treat it to remedy issues that the HAZ introduces. I'll try to explain it again because I've probably also confused others.

For example, when I deal with the castings I procure, we mandate that the supplier either repairs them prior to the heat treatment stage or they must be fully heat treated again after weld repairs. This helps resolve the otherwise brittle HAZ. You can do this, because castings are usually quench-and-tempered, which is a relatively slow process.

Welding stuff like Bis, Weldox, etc. requires both pre- and post- heat treating in order to let the weld form and also address the HAZ properly afterwards to restore its strength. You can do this because the processes to heat treat it are traditional and relatively slow. This lets you get (somewhat reduced compared to the parent metal) structurally sound levels of strength out of the weld locality. Because of it, Weldox and Bis both see widespread use in truck bodies, crane arm trusses, etc.

This is in constrast to flash bainite, which relies on it being a very fast process. By virtue of it being a fast, tailor-made process you can't just do it to a complex geometry. By welding it, you dump heat into the weld which then air-cools slowly as the weld cools, completely running counter to the flash bainite process that is necessary to produce the strength. That's why you see a halving in UTS in the mil report I linked in source 3 of my first post - you simply can't recover from the slower heat-and-cool process without doing the whole treatment again, and you can only do that on easy geometries (it seems).

As said, if I understand what you're saying we're essentially saying the same thing, but I think I phrased it quite badly in my post. Not that you disagree with me, but it just made me realise that I don't think I worded it well and wanted to clarify.