Chris,
I fear you do yourself a disservice. I don’t know whether you’ve ever tried to build a top end kit (basically Martin Finney or his successors, or something very similar) but if it’s a good kit, it fits together properly and there will be no glaring gaps or bits that don’t fit. Unless you’ve gone wrong, of course - and then it’s obvious - which is a good thing. RTBM, assuming the BM is legible and useful and relevant.
Making a decent job of a crap kit is hopefully marginally less work than scratchbuilding, witness Mickoo & Nick D’s threads on here, amongst others. It takes time, and you have to have developed some skills (aka, have made mistakes and learned from them) and you need patience, and time, and persistence, possible some specialist tools, and maybe a deal down at the crossroads at midnight.
Your buildings are at the very top. Whilst I accept that what you do so well is a different set of skills from building a loco, I figure that if you can learn to do that, I’m pretty sure you can build a decent loco kit, given a few pointers, and some support along the road.
I have ranted on here and on RMW about cheap, actually, crap, kits. They put people off, and it’s not fair, because the poor punter thinks it’s their fault, but actually, it’s a kit designer who couldn’t be bothered to do their job properly, and who gets away with selling stuff that is not of “merchantable quality”. Easy for me (and others, Nick & Mickoo are not shy) to say “j’accuse”, but far more difficult to prove.
in short, don't say “I can’t“, say “I haven’t yet”, if you must!
OTOH, if you want today “I don’t want to”, then that’s a very rational choice. What was it Gandalf said about “having to do the best with the time we have”?
atb
Simon