Depends on how you want to use it I guess. The 6D Mark II is indistinguishable from the 5D Mark III to my eye and not much better than the 5D Mark II. I wouldn't buy a camera with that kind of performance in 2019. The way I sling around gradients in lightroom it just doesn't work for me. You have to look pretty hard to find an area where the full size sensor in the RP outperforms the APS-C M62 sensor in any meaningful way. If you normalize for size the newer sensor is in a different league entirely.The RP will have the typical FF high ISO advantage, more shallow DoF, and will produce sharper images ooc. The sharpness is somewhat irrelevant at low ISO where you can sharpen in post, especially against a 32mp crop sensor. But it will be very relevant at high ISO where crop is already behind and sharpening just emphasizes noise. Contrary to popular belief, the 6D2 / RP sensor has very good high ISO performance.
Unless you go high MP FF, those are the advantages of FF and the RP checks every box. DR is often mistaken for being a FF advantage but there are plenty of examples of crop cameras having higher DR than FF ones, and not just Sony vs. Canon. The M6 II likely has higher DR than a Nikon D5 (for example). Regardless, the one weakness of the RP for stills would be some of the "worst" DR for a shipping camera. "Worst" is in quotes because as I've shown in this forum with a mere 7D there's still plenty of shadow recovery even in the "worst" sensors.
The M6 II will resolve more detail at base ISO (32mp vs 26mp) and will have a DR advantage, in addition to its feature advantages (video; high FPS; higher performance AF).
I think if I was looking for a budget stills mirrorless I would rank the RP above the M6 II by a hair, and that's in part due to RF glass access. Problem is for another $300 gray market you can go 50mp FF, which is a very large IQ jump. You just have to live with a 'flappy mirror'. But you also get professional AF, 5D build quality, long battery life, OVF IQ, etc.
If I was looking for a stills/video hybrid then I would rank the M6 II much higher than the RP. From the sample videos I've seen the 90D / M62 produce sharp, excellent 4k footage in both full sensor and crop sensor modes.* And the M6 II has DPAF across every mode except the 120fps HD mode which the RP doesn't even have.
* DPReview's video test comparison tool makes the 90D/M6 II look very poor at 4k compared to, say, an X-T3. But I've now had the chance to review several 4k sample videos and they look as sharp as the X-T3 or A73. Right away when I viewed the DSI Pictures sample video I was impressed as it had the same crisp 4k detail as the others, even at high ISO. At this point I have to assume DPReview did something wrong or used a poor lens. The X-T3 is still the better cinema camera (4k 60p; higher bitrates) but if you can live with 30p @ 120Mbps the M6 II's output is gorgeous.
Of course, if shallow depth of field is a priority than go with the biggest sensor you can afford. But that being said, baseline ISO for that sensor is not that good by current standards. I'd either get the m62 or just bite the bullet and step up to the R if you want the benefits of the new RF mount.
I was just talking about stills. Every time I act like these cameras should be able to shoot video I get flamed so I don't even bother with that anymore.