Fastmail vs iCloud mail

I wanted to pick email power users brains on potentially a better workflow to email than what I’m using. Right now I use apple mail on mac, and iphone to separately have all my varying email accounts logged in which consist of:
-Primary custom domain email, currently routed to icloud
-6… yes 6 google/google workspace accounts for various things. Most of these are inactive 90% of the time but I keep an eye on them. One of them is a notifications off throwaway/spam email account

I did a trial of Fastmail and liked the interface, but where I’m already paying $10/month for icloud it might be more sensible to leave the email routed through them? Those who have multiple separate email accounts, what has worked best for you? Is having Fastmail pull them into one inbox the better method? Or is standalone mail clients the best?