"A vanity domain you pay for, then you can redirect as you want and noone will be any the wiser."
Nothing vain about it. It's just a more practical solution. If you have your own domain you can move ISP without disrupting your email contacts.
Some years ago my formerly very good ISP fell into the clutches of TalkTalk. At that time I'd used the ISP email. I moved to a new ISP but to prevent a recurrence of the inconvenience of that happening again I registered a domain with a registrar who provided an email service. After my new ISP fell into the clutches of Sky I switched to another ISP.
I also found that eventually my original choice of registrar started getting outages which they never troubled to explain - and seldom troubled to acknowledge to I transferred the domain and email service to another registrar/email provider, again without disrupting my email address.
The other side of having your own domain is that you can set up and tear down addresses as necessary. Anyone I expect to deal with on a regular basis is given an alias I've set up specifically for them. If they start spamming I simply drop that alias; in fact I've the option of setting it to bounce email with a message telling the sender why they're being bounced. I also set up aliases which will only last a few weeks and anyone who doesn't, in my view, need a long term alias gets given the current one of those which will be pulled immediately if it gets spammed.
For a few quid a year you can have a flexible email service that's not, on the one hand, tied to a service provider you can't dump, nor, on the other to a big corporation who treats you as their product.
I have a Hotmail address for situations which demand an email address but where I don't expect any interaction whatsoever and that's treated as /dev/null and a gmail address if I need a Google login which carries no traffic at all.