Ok, well, to make a constructive argument that is less U NO U...
I think we can all agree that Mercenary solos represent a degree of power above average compared to most faction solos. This because... like 99% of them are characters, and characters get access to special abilities and stats on account of being FA C. ( that's my theory anyway )
Now, would similar solos existing in each faction be better than mercs that fill that spot for every faction? I think sometimes yes, sometimes no.
We don't really need a McNaile for every faction. Wouldn't make too much sense. But I think the hierarchy of Power Booster solos is a fair representation of the idea. You can argue that certain solos are undercosted or whatever ( The WW Siren is typically considered as such ) but that doesn't change the core concept - that each faction can have a solo that fulfills a similar role but with their own unique sculpts, stories, and playstyles.
We don't all need an Eiryss for example, but a toned down FA 1 or 2 faction of that kind of solo isn't too bad an idea. Less powerful, but less restricted at army construction. Can be used across multiple lists, and then removes upkeeps or messes with warjacks or whatever. They don't have to have identical abilities - just the same general role or idea.