^^^I think he's talking about raw kratom itself. Of course these days, some people actually do consume 7-hydroxymitragynine in its isolated form. This is something that was essentially unheard of a few years ago. That said, the 17x figure listed on Wikipedia is based on experimental data. In humans, when taken orally, isolated 7-hydroxymitragynine definitely doesn't feel anything near 17 times the strength of morphine. Keep in mind that that experiment was only measuring how tightly it binds (affinity) to the MOR opioid receptor, but now how effectively it activates the receptor (efficacy). So the 17x figure doesn't mean it produces narcotic effects 17 times stronger than morphine, because in reality 7-hydroxymitragynine has high affinity but low efficacy for the MOR opioid receptor.
Based on my now extensive (too extensive) experience consuming isolated 7-hydroxymitragynine, I'd say in terms of actual analgesic/narcotic effects, 7-hydroxymitragynine, when consumed sublingually & orally, is perhaps half the strength of morphine. So not 17x but rather .5 times. But this estimation is hard to make because it's comparing apples to oranges. Because 7-hydroxymitragynine has low efficacy (activity) at the MOR opioid receptor and as a partial agonist, has a dose ceiling, there is no amount of 7-hydroxymitragynine one could consume that would equate to a very large dose of morphine. For instance, the effect of 500mg of morphine cannot be reproduced by 7-hydroxymitragynine.
But I think the real question being asked here (by the OP) has nothing to do with isolated 7-hydroxymitragynine (and my apologies for further derailing this thread myself by going on about 7-hydroxymitragynine). I believe the OP is talking about kratom itself, the powdered, raw leaves of the plant, consumed orally.
So while keeping in mind that comparing kratom and morphine is a bit like comparing apples to oranges, if one was forced to convert raw kratom powder to MME (aka morphine milligram equivalents), I'd say 5g of kratom is equal to very roughly 5mg of morphine. But generally, MME's are used to compute a daily dose equivalency (for instance when someone taking 80mg/day of oxycodone is hospitalized or entered into a methadone clinic, that 80mg/day will be converted in MME's, which that this case would be an MME of 120).
So if someone takes 50mg of kratom they have an MME of perhaps 50, or maybe 60. The issue is, kratom, in its whole plant form, is more than just an opioid, it acts on adrenergic and serotonin systems, N-type calcium ion channels etc.