The biggest lie in quant finance is that you can do everything required at the highest level of a model. This includes data engineering, model development (quant research), implementation (quant dev), and be the end user (often a trader or operations team). This full stack quant does exist however they are never the best at everything and they often work in a very specific niche. Examples of a niche could be, auto loans, equity HFT, commodities, securitization, or etc. The systems, languages, math, stats, financial theory, and business uses are all different.
I would encourage people to focus on one main area (data engineer, quant, quant dev, or business user) and dig as deep as possible. There are a lot of topics inside of each of these and it is easier to jump around business types than to try and cover too many areas with non-overlapping skills.