In my opinion this is a truly terrible path to choose, but you will earn more than anyone in tech who doesn't win the startup lottery.
For juniors coming in, "messes of legacy code" probably isn't the best learning environment from a tech skills standpoint.
For more sr folks coming in to "message of legacy code", you do need to be a good engineer, because you may have to be working around a lot of stuff that can't be changed. You may not have version control. You likely won't have any sort of fancy CI/CD/pipeline process. You may not have tests (as the code is likely untestable in its current state).
Those sort of problems are more on the product side, along with the regular slew of product development tech problems. On the infrastructure/platform side (where I work) it is remarkably close to "regular tech". Same types of distributed systems problems, database issues, CI/CD pipelines, engineering efficiency, etc. The "new" part here is working with the finance specific areas such as physical data centers and networking to clients, or domain specific items such as data retention for compliance.
There's quite a difference with what I think of as pure-finance, companies that aren't producing a tech product, but are using tech to make money with financial services, or betting on the markets in various ways.
As for the problems, I was once in an interview given a coding task of moving money around a network of companies based on tax rules. Fun.
Any reason why it’s a terrible path to choose? Am I stunting my growth? I was hoping HFT would help leverage me into a big tech company for systems level stuff since (at least I was told this as a selling point to get me to join) its tougher here so FAANG likes to see HFT experience. Is that not the case?
These reasons are not universally applicable, so see what fits your experience, but... code quality is often poor, internal practices often seem to leave a lot to be desired, company culture does not seem to be a focus, assholes seem to get rewarded.
You can probably get into big tech from it, but perhaps not at the seniority you might expect, or if you do you may find it a struggle to get onboard with industry norms around engineering process and company culture that are missing from a lot of finance companies.
Base on what I can gather from my friends who work in the space (DRW, Citadel) it's just more stressful and has more politics than my current role (ML Engineer @ a retail company). Trading income for work-life balance and stress, and maybe OP is hinting that as you progress down that track the WL balance and stress only increase.
Just my 2 cents and why I didn't choose to pursue that path.
I think people may be concerned because these days it's more niche, though it's still a very common language. Take a look at the job postings from the companies you want to join and see what skills they want. Get familiar with some of them, even if you don't do them professionally.
Get good at the Leetcode style questions.
Are you doing distributed systems work? Can you answer design questions like: design bit.ly, Twitter, or Facebook? There's a lot of info out there on how to solve these problems.
There may be questions about your ability to work with "big data". But that's also something you can pick up on your own, even if you aren't doing it at work.
Look for technically challenging projects at your job and solve them. Learn from them. Think about ways you could have solved them better with what you know now.
i don't want to get shouted out by a bunch of coked up psychopaths.
Nowadays, it's quite different. Gifts have to be logged so people don't do it much anymore, metoo happened, and I can't really imagine another burger eating contest, even though that last one is fairly tame.