Hi Greenerlife - that usually happens to me too and when it does I think I won't bother again next year. This year though I planted sets through black weed suppressing fabric, having first dug in lots of sheep manure and seaweed meal. Some weeds appeared but I couldn't really see what was happening with the onions themselves as I had cut the holes too small so only the leaves came through. When I went to lift them I had a lovely surprise as great big onions were hiding under the fabric. I have grown them through black polythene before and that worked ok but difficult for them to get enough water. The weed suppressing fabric seems to be the answer for me. I also planted some bought onion plants, which arrived a bit late and, like yours, they are hardly bigger than sets, so a waste of money - that was through the fabric too, so it's not a miracle. Better luck next year
Now with the apple windfalls and some of the onions I'm going to make chutney