I was constantly lied to and pressured when I was in sixth form that I should take my LSE economics offer instead of reapplying for maths because Econ at uni is "bAsIcaLlY aPpLiEd mAtHs". I'm not sure if its because they are mathematically challenged and therefore it seems a lot for them, but the maths is so basic, its essentially just basic differentiation over and over and over, and the econometrics side is also just watered down statistics.
It is nowhere near as rigorous as a degree in maths, physics, CS, engineering etc, in all of which people are deemed very smart to be doing, and for good reason because the maths is actually challenging. But economics graduates are not seen as such, and I agree, because quite frankly it's a trivial subject compared to something like maths. Ironically, the hardest thing about economics is the intuition because most of the time it is not based in reality whatsoever.
Also, this is the most compelling reason: an engineering, maths, physics, CS graduate can do a masters, PhD in economics, but an undergrad in economics cannot get you anywhere near those other fields because it is just not mathematically rigorous. Also, an engineering, maths, physics, CS grad can do anything an Econ grad can do, and could do more and probably be better at it too. Plus, they're more respected.
So to summarise if you do fm and have good predicted grades etc, please do a quant stem subject (math/CS/Eng/Physics etc) instead they are so much more respected, and will actually challenge you and provide useful knowledge and skills. Otherwise you are wasting potential doing a second rate, laughed at degree.
Everywhere I look when someone is comparing, say, engineering to economics, there is an absolute majority saying engineering is miles above economics in terms of difficulty, its just not seen as a rigorous/respectable degree, especially because every finance bro wannabe in the country does it, which also further tarnishes the name of "Economics" because, quite frankly, I see some quite academically challenged/unserious people choosing to study it, lets just say that.