Hi,
I believe the theory behind this is that rich soil leads to lush growth of foliage at the expense of flowers.
My allotment started off as a cutting garden 11 years ago. It has evolved into a no-dig potager style garden, with some beds dedicated to flowers, some to fruit and veg, and some where flower planting becomes part of the crop rotation plan.
Like you, I was at first worried about the quality of blooms from the beds that I dress more generously with compost. However, flowers grow strongly and flower abundantly – and I think they sometimes do better in the “richer” beds, especially in long dry spells – as they probably have access to better reserves of moisture.
A major confession – I have never managed weed free no dig! This is partly because I rely on annuals (and some biennials) self seeding. These volunteer plants are much more vigorous than those from seeds I sow and provide many more blooms. I notice this especially with sweet rocket, cornflowers, calendula, ammi, and cosmos (the latter has no problem at all with self propagating and flourishing in compost rich soil!). Sunflowers, reputed to be greedy plants that leech all goodness from the soil, benefit from the conditions that no dig can provide, as do sweet peas.
So if my experience is anything to go by, rest assured your cut flower garden should thrive on no dig. The added benefit is the wonderful variety of insects the blooms bring to the garden – as well as comments from appreciative passers by.
Best wishes