The effectiveness of CT logs isn't a thing unless the website uses CT monitoring or is a huge company. A [delegated or non-delegated] DNS takeover, or IP address release (eg. cloud providers re-assigning an IP to another customer) could allow you to generate a certificate for some-forgotten-subdomain.medium-sized.company.com using the ACME http challenge. Of course this is mitigated by properly managing your DNS, and CT monitoring is encouraged everywhere.
In other words, the effectiveness of the CT logs is a thing. There are multiple services which will do this for you for free (Cloudflare and Facebook at least make it trivial to get notifications for your domains) and it’s a level of visibility which almost nobody had just a few years ago.
crt.sh offers a RSS Feed, I use that to track all certificates issued for my domain. Doesn't really need anything expensive or complicated.
CT Logs don't mitigate any of the attacks but they make them very very very visible if they happen. Especially if a CA goes rogue, this will be immediately visible and provable.
IF you pin services to a key you control this mitigates the problem with bad guys obtaining bogus certs, BUT now you need to manage the pinning application to ensure it knows about any new keys before they roll into use. This may force you to compromise on your rotation schedule, maybe you'd prefer to use new keys for the new cert you're buying this week but alas the new app version is still waiting for Apple sign-off, so it'll have to be next year instead.
IF you pin to an intermediate key, which is under the control of a CA, then bad guys who obtain certs from that intermediate will not be inconvenienced by your pin, but these keys are intentionally long-lived (they are protected in an HSM) so the rotation issue isn't as fraught.
