Q.leggy black eyed Susan
my black eyed susans are in the front of the house exposed to full sunlight at least 7 hrs of the day there are a lot of them but the flowers are very tall and fall over my neighbours are standing upright and look stronger. I mulch in the winter but I have never thinned them out in 5 years that I have had them. The purple ones and also the daisies follow suit.
Certified GKH Gardening Expert
It is very helpful to the plant to deadhead it at least once per season, although you can do this more times if needed. This article will help: https://www.gardeningknowhow.com/ornamental/flowers/black-eyed-susan/deadheading-black-eyed-susans.htm