Those numbers are for the "ad free" accounts, which are really lightweight anyway. For instance, the ad free accounts only get 100MB of storage for their email anyway, so a 60MB hourly cap is not entirely unreasonable: that's more than half your mailbox. Of course, for 40 cents a month, I think those numbers are pretty reasonable.

More appropriate would be the "full" accounts, which have a much more reasonable 300MB/600MB hourly/daily data quota. Of course, again, mailbox storage is limited to 1GB there... and so on.

I don't think the quotas are unnatural given the relative mailbox sizes. But, for full disclosure, I am a (happy) Fastmail user.