How do you plan to change emails? I'm thinking of moving out of Gmail too but didn't decide on a service yet. Office 365 with Exchange sounds good but it's like moving from one monopoly to another I guess.
I am becoming concerned about the power Google has over my life (have been for a while). They know what you're reading (Chrome, even in incognito mode via DNS), what your thinking (web searches), who you're in contact with (Gmail, Android + their Apps), not to mention maps and what they do with your photos/ drive data. Even patient data with the NHS sharing data with Deepmind[0]. The company needs to broken up as the Did with Microsoft years ago.
I didn't have big problems with it, except for a monthly student loan payment confirmation email that fastmail refused to classify as not spam no matter how many times I so marked it.
In general, I found gmail's spam filter to be the best. If, however, you don't need to regularly interact with lots of new email addresses, fastmail will work fine for you.
This might be fine for some or even most people but if like me you’d prefer to spend less time on email not more it may not be the best choice as an email provider.
Nothing against the service, just be prepared to manually train a spam filter
Also, Gmail definitely has a problem with false positives. At the small agency where I worked a few years ago, a lot of our internal company emails were ending up in spam folders. It got so bad that I had to go around adding our company email domain to the spam exclusion filters just to make sure that my co-workers were receiving my emails.
I'm not attacking Fastmail. I just didn't want to put in the effort to train the spam filters.