I would agree with that, if it's to be means tested then do it right and investigate where a decent cut off (not causing hardship) point should be, of course this is to much like hard work for them so took the easy option of using Pension Credit/benefits as the means test,, which will leave as you've said those just outside of qualifying for benefits losing out and some will be finiacially worse off than than those receiving pension credit plus winter fuel allowance.
Although they state 880,000 folks can apply for pension credit, no way they will be able to process that number of pensioners before winter, probably take a year or two to get through those sort of numbers. So this process should have been completed before stopping the WFA.
It's also a strange policy to make savings as if those 880,000 apply and get pension credit it'll cost more than the savings from cutting WFA, £1.4 billion saving as against £3.4 billion to fund 880,000 extra receiving pension credit.
The reason i think this was done in this stupid fashion is, it's a long standing aim/ideology of Reeves (prob labour as well) to hit well off pensioners (non labour voters on the whole), so as soon as they are in power swing the hatchet without thinking through the consequences. Their dislike of well off pensioners blinded them from seeing they were affecting the lower income pensioners as well, or maybe they just don't care as long as they get their free clothing, holidays etc from rich friends/donors/business and thousands in energy allowances/expenses courtesy of tax payers.