SPF record ends with +all — why this is worse than no SPF at all

The terminal all mechanism decides what happens to senders not matched by anything earlier in the record. +all means "pass" — an explicit statement that every host on the internet is authorized to send mail using your domain.

This is not a weak configuration, it is an anti-configuration: it hands spammers a valid SPF pass. It is nearly always the result of copying an example or misreading the qualifier syntax.

Change it immediately. There is no legitimate use of +all on a domain that sends mail.