The RF 24-105mm f4L IS USM is better than its EF cousin but you would not want to live on the difference. The RF 24-240mm f4-6.3 IS USM is not the greatest example of optical excellence. Yes both lenses are at the lower end of the RF price point but they have not moved the bar.
It remains to be seen how good the RF 100-500mm will be with & without the converters but for almost 40% more in price it needs to be really good to justify that price hike.
I think you're confusing my messages and replied to the wrong one or are combining my thoughts.
Previously I used the reference to the 24-240 to show that even in the worst-designed (IMO) RF zoom, the telephoto end is really good. That was when I was talking about the new RF f/11 primes that are around the same price point, trying to make the point that I think the IQ will be pretty good. Summary: if 240mm on the 24-240 is really good, the f/11 primes should be even better.
The exact quote I made that you referenced was about the GF 250 + 1.4x – That was only meant to speak to how the IQ of TCs has improved in the last few years plus how much better they are being designed for mirrorless than they were for DSLRs. Summary: Using higher-end mirrorless TCs can be more like having a modular lens with very few sacrifices (if any) in IQ.