Commodity/Power trading outlook

There are several questions within your post, so it is difficult to give you a short and comprehensive answer. I offer my two cents below, having been in commodities trading (oil, power, gas, carbon) for several years, but still it is just a personal opinion.

I have not worked in BB S&T, so take with a grain of salt, but from what I see and hear, the level of automation is severely lacking in many commodities markets. As you suggested, this presents many opportunities and lower risk of trade execution being automated, but at the same time it can be very frustrating, seeing how inefficient some things are. In terms of headcount, commodities industry is quite small, so overall there are less trading seats available compared to financial markets. That is a potential downside.

Education - you can find people with very varied backgrounds in the industry, so there is no standard template. Quant subjects, or Econ + applied math that you are considering are for sure good and will not hinder your chances in any way.

Career path out of uni - I have the feeling that getting a commodity trading seat is more difficult and less straighforward compared to banks, where the career progression is more structured and there are more places for grads. Joining TDP is usually the most direct path to commodity trading seat. Difficult to get, though. Other than that, aim to get a foot in the door in any position in the industry, as close to trading as possible. Once there, being good at your role, making life easier for traders and being generally likeable is best way to get noticed for potential move to junior trader, once such spot opens up. For many people it never does, by no fault of their own. Just bad timing/luck. Easy to get pigeonholder in ops/support role and difficult to hired as trader in different company without prev. experience.

Career progression - once in trading seat, essentially the only thing that matters is making money. Not much of progression beyond changing titles (junior/senior), which come with larger risk allocations, potentially getting "better" pick of regional or product coverage as you get more senior. If you find yourself at a good place that works with your trading style, milk it as long as you can. Hours in general are not bad, I would say you can get by with 10-11h days on average. But outside of that being on call is common, depending on the specific commodity. On top of that, you will usually think about the market, read, learn new stuff etc. but I would not consider that work, if you enjoy it.
Lateral move to different company (or type of company, e.g. trading house, major, utility, HF, bank...) is most common exit for traders. Changing commodities is also sometimes possible, most often during specific market cycle periods. Some people transition to management role, but that requires different skills and also has it's own challenges. I personally don't know many traders over 45 years old, so I guess there is some point when either you A) make enough money to consider leaving, or B) make too little money and are forced to leave. There are of course exceptions when people want to keep trading and are able to maintain their edge.
Ex-traders are normally able to find other roles within the commodity space that value their experience and connections (e.g. portfolio/asset roles in industry, consultants, IT trading tools providers, analytics companies, strategic advisors, brokers etc.).

When it comes to choosing BB S&T or commodities, there is no easy answer. If you have options, pick the one you are genuinely interested in. I personally see the future brighter in commodities, but I am obviously biased.