I don't understand why you think stating facts is "emotional irrationality". The 800 and 1200 are literally EF lens designs with an added 1.4x or 2.0x teleconverter group. Furthermore, Canon never developed these lens designs for dual mount, aka mirrorless, as you claim. They were quoted as such in a DPReview interview right after launch:
"Were the EF 400mm F2.8L IS III and 600mm F4L IS III developed from the outset with the intention of being ‘dual mount’ designs, for both EF and RF?The EF 400mm F2.8L IS III USM and EF 600mm F4L IS III USM, which we released in 2018, were manufactured to an extremely high level of perfection in order to realize high image quality, light weight and high-performance IS. However, we did not develop these lenses with the intention of making them 'dual-mount.'"