That's carefully avoiding another few issues, though
WhatsApp did not start out as being secure - as a matter of fact, the very first thing it did on installation was to ship the user's address book to the WhatsApp servers (it won't even work without having that access) - that was possibly the data that convinced Zuck to pay a lot of money to buy it.
Now it is "secure" - in other words, security has been retrofitted, never quite the best option.
Next we get the owner's business. Where does FB make its money? User data and advertising. In other words, you have an application, offered for free, which is in direct conflict with the aims of its owner (and the government in that country). That's not a very good argument to trust it IMHO.
Signal does not have that conflict of interest at the very heart of its operation, which is why I would choose it if I didn't use another solution (no, not Telegram - not found of it broadcasting who joined now because it means it keeps re-checking a list).
So, nice letter, but not entirely in agreement with the argumentation.