> The end client should be the one to determine status and shoulder the responsibility if it turns out to be incorrect.

I'd say the opposite, the incentives / risk structure are otherwise completely misaligned. If the end client says you're outside IR35 and you should be in, they get whacked for income tax + 2x national insurance (employer and employee contributions). If they say you're inside and you should be outside they only have to pay the employer NI contributions.

That's a recipe for blanket "inside IR35" decisions, which is exactly what happened to the detriment of many genuinely independent contractors.