Skills you learned in PE

If your goal is to start your own business you don't think it'd be a better idea to work at place the owns and operates businesses than at a broker? Even if your day to day activities are prices driven you're still in those board meetings, strategic planning sessions, etc. soaking up knowledge that would be useful to an operator. Just because the tangible excel and ppt skills are similar doesn't mean the intangible learnings are the same.

If your goal truly is to start your own business, then I strongly believe that PE would be a better place for you than IB. A few reasons/thoughts about why below:
 

1. Similarities: Both roles involve financial modeling, due diligence, deal execution, and interaction with clients/LPs and other stakeholders (owners, etc.)
2. Investment analysis: In PE, you'll develop a deeper understanding of investment analysis and valuation. You'll be involved in assessing potential deals, and you'll gain experience in understanding the intricacies of various industries and business models.
3. Portfolio management: As a PE associate, you'll have exposure to the management of portfolio companies, which includes working closely with the management teams of these companies. This can provide you with valuable operational experience and strategic insights that are not typically part of an investment banking role.
4. Long-term value creation: PE firms generally have a longer-term focus on value creation, as they hold investments for several years. This perspective can help you develop a more strategic mindset that may be useful when starting your own business.

Personally I find that #3 and #4 are the ones that have been best for be as an emerging businessman, and have given me the confidence that if you dropped me into any LMM company, I could take over as CEO and have it running better than when I found it within a year. IB is great because you get the hard skills down and you see a lot of companies, but actually getting your hands dirty is a far cry from what banking teaches you. PE isn't getting your hands dirty either (technically, nothing but actually operating is) but it IS a lot closer. 

Your instincts are right that, with the end goal of ultimately starting something, mega cap PE has few advantages compared to IB. Arguably the biggest differences will come from the small idiosyncrasies of both situations (your specific IB team and a prospective PE team). Depending on the IB team and the PE team, you might see a greater variety of business models in IB than in PE. Unless you already have a specific business in mind, getting exposure to a variety of business models and industries can be quite helpful. Likewise, you will still get exposure to management teams (the clients) working in IB. Generally, on a sellside deal, you can get a fair amount of exposure, although this depends on your banking team, the client, and the deal.

I think the story that UMM and megacap PE tell of learning how to be an operator and rolling up your sleeves with management teams is largely BS. You're still a process monkey and resource. It is what it is. Perhaps in LMM PE, you get more of that hands-on operational experience, but I've never had the experience personally.

The only way to learn to run a business is to run a business. All PE is going to teach you is some financial technicalities which honestly will not be applicable to your "own thing" (too small in scale), at least in the beginning. 

Soft-skills, correctly judging people, finding what makes said people tick (principle-agent problem in a nutshell), and the ability to execute with minimal/constrained resources is what will matter down the road. 

Edit: PE will let you build a small nest egg though, so save diligently and don't blow your salary on frivolous bs (if you are serious about starting your own thing). In a few years you can have a 50k runway to start off with. Good luck.