The amount of time and overhead you have when encrypting on write or decrypting on read is the same for an SSD or HDD. So you're adding the same time lag and CPU overhead in either case. Only with an SSD the time lag is a greater proportion of the total time lag. Also, encrypting a sector means that SSD firmware can't compress it, which some would do. The argument you gave just says... that SSD's are faster. That is not news.

Also, the SSD firmware stores much more metadata about access patterns, which could revert your efforts at keeping your doings private.