You seem to use an old admin version, since the bug has already fixed on DW9.10.15 and up by task 4498 (deleting shop/group has many products). The method mentioned in the exception is not used now at all. I've tested the feature with deleting Ecom/PIM product group has many products (> 2700) on last DW9.12.7 and was not able to catch any issue.