I mean, I can fully understand that breastfeeding is at times shown as this idyllic feeding directly from the breast, calm serene mummy and happy thriving baby. When in reality, breastfeeding looks like so many different things like exclusive pumping/ combi feeding etc and it can be a real struggle. So if your experience of it wasn't positive, then I think it's great you felt able to promote your mental health enough to decide on formula second time round.
However, I don't think it's fair for you to then criticise other women for making different choices to you. Breastfeeding isn't a complete panacea, we know that breastfed infants will still get sick/ have health conditions etc. And we also know that formula feeding isn't awful, and formula fed children thrive and do great. Using a few anecdotal examples from your lived experience and presenting them as 'proof' is really misleading. We know from research that in general, breastfed children do better academically and that is linked to the length of time they are fed for. We know that there are certain health benefits for mum such as reduced risk of diabetes/ certain cancers/ heart disease etc and again these benefits are linked to length of time they feed for. We know that immunity and allergy are two different things. So while yes, your bf child may have lots of allergies that doesn't actually speak to his immune system. A lot of allergies are actually hereditary. Parents with allergies are more likely to have children with allergies. Breastfeeding won't change that. What it can do is support a healthy immune system at the time in a child's life when they are most under attack in that respect with starting nursery etc. If children aren't sick as often or for as long (because we know they will get sick) then that benefits our economy. Helps women stay in the workforce when they are predominantly seen in a caregivers role. These are all perfectly valid reasons for someone to decide they want to continue feeding when it's working for both them and their child. And equally none of those reasons should be used to undermine women who decide to stop earlier or decide not to breastfeed at all. Women having the right to choose what works best for their body, their family, their baby is how we empower mothers. Not attacking their choices, giving them incorrect information based on two peoples experiences and name calling.
I'm sorry that you maybe had a rose tinted idea of what breastfeeding would be like and what it would mean, I think that speaks a lot to the lack of clear education and information around breastfeeding in the UK -it really isn't good enough and it lets a lot of women down. I'm sorry that you feel disappointed that you didn't see the benefits you hoped you were working for. But you can't use that as a means to put other women off. And comparing two individual children is not a wide enough pool to be basing the comments you are making off as your specific situation is at odds with the majority of research on the subject. But again- that's not really surprising since the research shows breastfeeding is not a 100% guarantee.
For me, hearing that other women have fed for longer periods of time has really helped me reach 11 months with ds with no family support and a lot of pressure from the beginning to switch to formula. While it might be weird to you (which if I'm honest i think is stemming from your own negative personal experience), for a lot of us it's reassuring and motivating since breastfeeding is hard.