After checking your stats, I have to question your definition of 'reasonable sim racer'. I'm pretty sure your definition is different to mine so you really need to look at yourself before looking for things to blame.
Find time to practise more and get some consistency under your belt. If you're still way off, look for tips on youtube. Plenty of good track guides out there.
I don't know if subliminal messaging is involved here but watch a lot of the tops driver's videos as well, especially the practise as watching the correct line lap after lap soon sinks in. I watch kie25, super gt, nicor, tidgney, z28 and eerieissss regularly and wish there were more. Great practise with zero effort.
Have a look at
@EERIEISSSS youtube channel too. Starts the story using a pad with all assists turned on, to a first wheel and the struggle to learn it and a quest for A+ rating. He's now a solid A rating and still improving.
https://www.youtube.com/channel/UCqPNuJUqqn9QBZiq1QEW_UA