Florist here....
In all fairness, those flowers would have come as a handtied and your Mum has cut the string and re-arranged them herself taking stuff out in the process. The vase is too short and the wrong shape for the height of those flowers. If you hold a long stemmed bunch at the bottom, the flowers will splay out widely at the top, which gives the illusion of being sparse. Hold the stems too near the top and they will bunch together tightly which will make it look smaller.
In floristry, you pay more per stem for quality and length. The price differential can be substantial. It's why supermarket flowers are so cheap because they are generally short and low grade flowers plus the supermarkets have huge buying power. Some farms will sell all of their stock to a supermarket which will hammer the price down even further. It's like comparing Tesco Value Sausages with Waitrose fillet steak.
Those flowers look like good quality. I would hazard a guess that the fireplace is around the two foot mark so they are also long stemmed. The flower list is...
Hydrangea x 1
Roses x 3
Lisianthus x 3
Delphiniums x 3
Chrysanthemum x 2
Foliage
They're all expensive flowers. I'm not working at the moment so a bit out of the loop on prices but let's just say I wouldn't be putting a hydrangea in a £35 handtied unless it was a few simple stems in brown paper because hydrangeas are £££.
Florist choice is generally the best option because a good florist will choose the best combination available for the budget. The difficulty is £70 can look very different depending on the flowers you use and the person who is making it. In the shop, some customers want quality (i.e. the Neptune ladies who lunch brigade) and some customers want size (generally most blokes who don't care if you use the cheaper stems). It's easier to gauge this face to face but unless someone specifically asks for a compact handtied, I try to make things as large as possible because people don't want to feel short changed.
Flower prices are insane at the moment thanks to Brexit and cost of living. It's a bloody hard way to earn a living and most florists earn either minimum wage or not much more. Lots of shops have gone in the last year or so because a lot of people just can't make the numbers work.
A really good florist an absolute joy to walk into but sadly the majority of the public have no idea what quality looks like in terms of flowers because they've been hypnotised by the car crash that is the supermarket flower stand.