Anyone else noticing that senior bankers are kind of stupid?

Maybe some are but most likely you're just reviewing their competence from a different lens than them

As analyst I used to get so annoyed at VPs and above who didn't understand the detailed minutia that went into each model/analysis, etc. and mistook their lack of focus on it as a lack of competence/understanding. In reality, as you go up to the mid/senior levels of banking you realize how much you have to focus on other things around project/client management at the mid-levels and bringing in business at the senior levels vs. minute details.

As others eluded to, your seniors were once analysts/associates too and if they dug in would probably understand it (being in banking 10, 20, 30 years you will see an unbelievable amount of reps) but if they spent significant time on complexities then they would not be able to do their actual role properly. They need to rely on their teams to filter the exact right amount of info for them to understand the situation and reflect that back to the client when asked (some are better at this than others...). 

By and large the MD role is about bringing in new business and providing their clients the right amount of exposure so that they feel the love while also leaning on their team to do the nitty-gritty execution. Your detailed analysis of beta or PF adjustments to EBITDA to a certain extent are not something they need to concern themselves with in more depth than necessary.