No. The regulation and that letter stop short of prohibiting, for example, one ham on sideband on 5403.5 and another on cw on 5405.0. Both stations on the same channel.
" ... Accordingly, NTIA requests that 47 C.F.R. Section 97.303(h) continue to require that amateur stations transmit only on the five center frequencies allocated to the amateur service. ... "
I think maybe you're right, based on that sentence.
I have some things I'd like to say in reply based on some other things I've read, but since I don't know where to find them, I guess I'll wait and see what the April QST says.
In the meantime, I'm certainly going to follow the NTIA's "request" as if it were definitely a rule. Their position in the rest of that letter is very clear: if we hear another station on a given channel, then they do not want us to transmit. They gave us those privileges, and they can take them away.
EDIT: I just found something new. The next-to-the-last paragraph says "Currently, 47 C.F.R. Section 97.303(h) requires
that amateur stations transmit on five assigned (center) frequencies."
What do you think?