I always started with cold butter and cut it into the flour, sugar and spices. To get a larger crumb grab handfuls of the crumb mixture and squeeze it as you add it to the top of the cake, some will hold together in larger marble sized clumps and some will fall as smaller pea size crumbs.
The old recipes call for you to add the dry ingredients and cut the butter into them and then set aside a cup or so of the mixture for the topping before adding the wet ingredients. That is the type of recipe that I used because it was a little quicker and less involved. If the crumbs are more important than the cake then I would go for one of the Entenmann’s copycat recipes. They usually call for a separate topping recipe. Still squeeze handfuls of topping as you add it to the top of the cake to make larger crumbs.