While I haven’t personally seen anyone use hitch pins for a channel coupling, I have dealt with many trailers with them being bolted with grade 8 bolts. I’ve seen bith scenarios there:
-Channel clamps the hitch tight. Usually you need a washer in between the hitch and the channel to take up the small amount of flex the channel has to get a tight clamp on the hitch.
-Channel is loose and has play between it and the hitch, even when the bolts are torqued tight.
In both situations I have never seen a failure due to load weight.
I have seen the grade 8 bolts fail once or twice, but seemingly due to being overtorqued. However when the bolt fails, the other one has always been intact still. I’ve never seen two fail together. Obviously best case would be for the top one to fail, instead of the bottom one. But either way as long as only one fails it should give you enough time to get to a place where you can fix it.
If you use your trailer a lot and don’t have a tight clamp between channel and hitch then you should expect eventual wear on the pins or bolts no matter what. Even if it takes a long time to see that wear. Either way you should treat your pins/bolts as a maintenance item that should be inspected periodically for wear.
I see no problem with using pins, but I would recommend higher quality ones, maybe reconsider the $2 HF Chineseium pins.