These myths are popular, in my experience they are not true.
I am speaking from personal experience. I've run my own mail server for about 15 years.
A few months I had to publicly complain on twitter about Microsoft blocking my email in order to get them to stop putting my email in the spam folder (after having to move to a new IP). Their support people before I publicly complained just kept responding with a form letter with advice for commercial senders sending transactional, newsletter and marketing content.
All major providers except Google were putting my messages in the spam folder by default despite me getting myself whitelisted in DNSWL and having proper FcRDNS, SPF, DKIM and DMARC configuration.
The IP was not in any reputable public blacklists, and the domain had been in use for many years.
I have seen Microsoft blocking entire /24 neighborhoods on the basis of a single IP sending spam.
You were probably hit by that as collateral damage.
Not really. It's not possible to send mail from a dynamic IP at all, and there is a lot of technical minutia to not get thrown in the spam folder for major providers. In fact, many major providers simply assume mail sent from an unfamiliar domain and/or IP is spam by default, and you will have to contact them to ask for permission to send to them.