Lower your tire pressure.
My rears are at 20 PSI now (filled). I've tried as low as 15, but it made no difference. I've also run the chalk test, and am satisfied with the contact patch I'm getting. The wear pattern on the tires (which now have 1500+ hours on them) also indicates a history of good inflation pressures.
The bare tires work great on dry ground or even somewhat soft/wet (I don't go out in my woods when it's really sloppy out). In snow, going forward on level ground or straight up a slight incline, they are just "OK". Hardpacked snow or ice, or snow on top of those conditions is another matter entirely. I can get around if the slope is not too great, but there is not a chance of pushing snow off the hills in our driveway. In bad conditions, even the slight crown in the driveway is enough to start the tractor slipping sideways. It was slightly better when the tires were new, and still had some edges on the lugs, but not much. As it is now, our cars get up and down the hills better than a tractor with R4 tires: AWD minivan w/snow tires, AWD Subaru with studded snows, 2WD Chevy Bolt with studded snows). The Tacoma with "All Season" tires has to be in 4WD to make it up if there is much of anything on the driveway.
If your bare R4 tires are working well for you in the winter, that's great. They just aren't cutting the mustard here. Perhaps our definition of "sucks in snow" differs. I doubt I'd be happy with bare R1, R3, or R4 in the wintertime, though I have seem where Turf is a bit better on bare ice, and Ag tires can sometime power through deeper snow than my bare R4 tires.
I still like the R4 tires for the type of work I do, but for ice and snow, I'll keep my chains, thanks. It beats being stuck out in the woods a mile from home on a cold winter day, or just spinning my wheels when clearing the driveway, or only doing snow removal in a downhill direction and hoping that I keep it on the road, because if I slide off, there is little chance I'm going to be able to back out uphill with bare R4 tires.