Much like bitcoin security practices, when it comes to any privacy set up (Tor, VPN, both, or something else entirely), it is usually user error which results in failure. Tor is obviously meaningless if you use the same email for both activities frowned upon by your government as well as your real information, as in your example. Another example which I've seen a couple of times is people forgetting to use Tor all the time. You only have to log in to an account, website, service, etc. once without Tor for them to be able to link all the activity on that account to your real IP.

If you are worried about a three letter agency having the resources to be able to set up and maintain enough Tor entry guards that you are likely to use one (and enough Tor exit nodes to be able to deanonymize your traffic), then said agency is not going to be stopped by a $5 a month VPN provider.