Price deflation is only of concern to debtors with fixed rate loans. For those with variable rate loans the rate will tend to drop during deflationary periods.
I agree, if the lender makes cheaper credit available, and if borrowers are automatically provided with drops in their loan rates. If borrowers have to shop around for a better deal and pay fees in the process, this would dull the effect of a lower base rate.
Some other reasons that the ECB wishes to fight deflation are described here:
Some other reasons that the ECB wishes to fight deflation are described here:
https://www.ecb.europa.eu/press/key/date/2016/html/sp160404....