Is private equity really better than investment banking?

I don't have nearly as many years of experience under my belt as it sounds like you do, but wanted to share my thoughts. For reference, I've worked in both M&A advisory and PE roles (as a junior), and it's been really rewarding to get to sit on both sides of the transaction. Honestly, although I know that PE analyst roles right out of undergrad are becoming more popular, I'd really recommend that people interested in PE do a stint (no matter how short) on the sell-side. It allowed me to gain greater perspective and has honestly made me sharper at understanding deal psychology. 

To my knowledge, at the senior level, the roles of seniors on both the buy- and sell-side are both very relationship-driven. On the buy-side, senior professionals are heavily focused on relationship management with the investment bankers/other financial service professional from whom they source deals. Principals and partners in PE are also often called on for conferences and roadshows when raising a new fund or presenting results to LPs. I used to think that the salesman role was exclusively a hallmark of the sell-side, though there is really a decent amount of that on the buy-side as well.

In my opinion, your non-traditional route into the financial services industry would actually likely make you highly sought-after in PE. Since the industry has grown so quickly and there is so much dry powder that needs to be deployed, PE firms are scrambling to find ways to make themselves the investor of choice to the companies they court. This marks a dramatic shift in the industry, as the space has become hyper-competitive and simply having the capital to get the deal done no longer cuts it. One of the strategies that many private equity firms employ is keeping operating partners on retainer who can help them navigate particular industries. These operating partners work with TargetCo management teams during diligence to demonstrate the PE firm's operational expertise and are often later installed into the new portco in a management or consultancy role. Of course, these operating partners are an extra expense to the PE firm, so someone like yourself would be a huge asset since you could serve as both an operational partner and an investment professional. At a MM or LMM PE firm (or any PE firm without a separate value creation team), you'd most likely also be able to get your hands dirty and work directly on portco strategy, which might be enjoyable for you if you particularly enjoyed your time in corporate roles. 

TL;DR it's a totally different ballgame to own the company and be able to set the direction of its strategy — whether by taking a seat on the board of directors, installing operating partners in management positions, or taking an active role yourself. Beyond just personal fulfillment / interest in the work, the asset class is becoming increasingly competitive, so it's more important than ever that private equity firms need to find a differentiation angle, like having operational expertise in a particular industry. Most senior private equity professionals have been in the financial services industry for their entire careers and are only able to see things through the investor lens, so the fresh perspective and wealth of experience that you bring would definitely make you an attractive hire.