oh, I'd totally forgotten the part where maltz says "you wouldn't use {law'} in these instances".
Finally, I understand what's going on.
For ease of reference, I copy-paste here in it's entirety the message from maltz:
For the archive: this is printed in qepHom 2017, page 17.
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{vItlh} means "be high, great (in quantity, size, intensity)."
It's used for things that are measurable or quantifiable but not
necessarily countable. So you'd use it for things like speed or distance
or the price of something: {Do vItlh} "high velocity," {chuq vItlh}
"great range, great distance." You wouldn't use {law'} in these instances.
For things you can count (like people) (as opposed to things you can
measure using units of measure, like length or speed), you'd use {law'}
almost all the time. But you'd use {vItlh} if the number of whatever it
is you're talking about is higher than normal or greater than before or
greater than what was expected.
So if you were referring to a lot of warriors, you'd most likely say
{SuvwI'pu' law'}. But if the high number of warriors is somehow
important, if it's the point you're trying to make and not just an added
fact, you'd use {vItlh}. You'd use it if you're not saying merely that
there are a lot of warriors, but that the quantity of warriors is
particularly high (higher than usual, higher than expected, higher than
some other similar group of warriors, etc.). So it sounds like L'Rell
used {vItlh} correctly in referring to the large number of people who
died in battle (more than expected, more than before, etc.).
Note that the exact number of warriors (or whatever) doesn't matter (and
doesn't have to be stated). The idea is that the high number of warriors
you're talking about is somehow noteworthy (the number of warriors who
died is greater than the norm for this sort of military unit, for example).
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~ Qa'yIn