Is IBD the best place to develop the best corporate finance/valuation skills?

Probably, depends on what you mean by really dissect a company.

skillset can vary tremendously from project to project. So definitely possible to go a year with less emphasis on valuation, but it’s all connected. Once you’ve been there for longer, you’ll start to see how everything comes together.

If by "value" you mean genuinely how much a buyer will fork out for a target, then I think there is no better place than an IBD buyside mandate to learn to do this because this is literally where people put the money behind the theory. I've been on a few buyside and sellside mandates now, and have come across a range of different Big 4 valuers, MBB mgmt consultants, and specialist valuation firms providing a view on how to value the same asset. But at the end of the team, it's the IBD team that's leading the financial analysis workstream on a buyside, and it's the IBD team that will be forced to defend the valuation. Unfortunately you have to get through a lot of other ad-hoc work (financial modelling, finding comps, building the CAPM) before you're in a position to be providing that thought leadership on the valuation (usually around D/VP level)

There may be some Big 4 val teams out there that do pure valuations, but to the best of my knowledge those are purely theoretical ie they don't get transacted upon. They're also not subject to the same level of real world vigour that the IB team would take their val through in a buyside process e.g. what will my competitors pay for this? What's the actual amount of debt my relationship banks will give me? What's the credit rating agency going to say about this?

There are plenty of disciplines out there that will say they do a valuation - there are very few that will back it up with money

I remember seeing a post quite a while back for a Q&A from a guy who transferred from Big 4 Valuation to IBD and he said he could model circles around his associates. I don't work in Big 4, nor do I really have any contacts in the space, but I don't doubt what he said. The short answer to your question would probably be that. Big 4 Valuation, D&P Valuation, etc, where your literal job is to value assets, companies, and transactions, without having to worry about the bigger picture.

Coming out of undergrad, I had similar questions. If the buyside loves modeling so much, why don't they just hire those guys? At the end of the day though, that's not how the world works and there's much more at play than just how good your excel skills are.

Depends a bit on the sector you cover but deffo IBD. Telco (if you have ever seen a tower operator model, you know what I mean :D), Mining, power, infra, etc. that can make you a real modelling god. There are sectors that are not as technical. I know a good amount of "corporate finance nerds" that love FIG exactly because of its very technical nature.