Back office (Ops) vs F500 Corporate Finance

I used to have a cushy job WFH in Corporate Finance at a F500 company. It took me a few years for me to perfect the role, but after I learned the projects' financials really well, it was a breeze. 

yea from everyone I talked to in corporate, the work is so much lighter than what you will be taught in school. most say you don't even need a degree for it..

You'll make more money and have more interesting work in CF than a BO role. Not saying CF is going to blow your socks off with work you want to sink your teeth into, but BO ops at a BB could be something as awful as managing a queue of the same request that takes 10 minutes and no thought day in and day out.

F500 probably more relaxed lifestyle 

since no one's going from ops intern to front office, is there any middle office groups where ops can make a lateral after a summer internship. I know a guy who started as Ops Summer analyst for JP, who was hired full time as a Trade Lifecycle analyst, to which my understanding is not back office. Thoughts?

I would implore you not to do back office. I did a banking internship that was largely MO with a part of my day that can be defined as a BO function, so I think I am fit to answer this.
If you enjoy doing the exact same thing every day, back office is for you. Some people genuinely like that and can get through their career with that. It’s not a particularly savory role if you’re ambitious to climb.
CorpFi will give you some solid exposure and while MO, you have a shot at potentially landing a group that works with FO, and can introduce you to better options.
I would highly recommend you choose the CorpFi role. I was in a similar position with corporate finance for AM vs operations at a top BB and I do not regret doing CorpFi instead.

BO is a very broad term.  I was at a big firm once where "Donnie from Risk" got a PM job on our quant team.  I also think I throw very intense questions at the performance team when I need the FactSet info I don't have.  Don't knock what you have, although the other option may be a better forever job.

Corp Fin all day vs back office ops.

However, if this is a group FP&A role, I’d try and lateral out as soon as possible. Nothing worse than financial reporting.

Corp Fin can be pretty interesting when at the enterprise level and in a strategy or at lease guidance role where the CFO is involved.