Straggly flowerbeds

I've noticed that a lot of gardens seem to be ahead of mine.  We have two south facing borders, on light sand, which are in shade for part of the day, but still gets a lot of sun.

In the spring the beds are full of forget me nots and bluebells, which I've been pulling out over the last few weeks/month.

They look beautiful, but I'm wondering if they are doing more harm that good in the bed, as now plants seem straggly and I've been realising that other people get their plants in nice round mounds and mine are all over the place.

My astrantia seems to be the only plant that looks good.

Would the straggly-ness (made up word) and the plants seem to be stunted in height be due to the light sandy soil and not getting enough water, although I did mulch with manure this spring or is it because they are late starting off because of fighting for light from the forget me nots and bluebells.

Any advice gratefully received.  thank you.