Izzy's behavior during OFMD 1x4 was exactly what he should have done as First Mate. Meanwhile, Edward's behavior was a failure of leadership.
The creative parts of leadership are 100% within Edward's role as Captain. He has the vision, he formulates the plans, he makes the decisions.
Meanwhile, as First Mate, Izzy's role is to execute those plans: cleaning up the details, taking any heat from the crew, et cetera.
What happened in the episode? Well...
Throughout the episode, Izzy asks Edward what the plan is to deal with the Spanish—a mortal threat against their lives.
When Edward's ultimate answer is that he's tired of the the same thing over and over, Izzy says that without a plan they're going to die, and Edward's response is, "Let's try that."
Izzy does the very fucking reasonable thing, as First Mate, of trying to get a plan together so they won't die. This is outside the purview of his normal role, but sometimes the plan offered to you by leadership is 'nothing' and you have to cobble together whatever the fuck you can.
Edward eventually reveals that he had a plan all along, but because of his refusal to communicate that plan with anyone, a critical error is left uncaught—one that Izzy catches the moment he has the opportunity.
Ultimately, Izzy's concerns are proven right, when Blackbeard's refusal to communicate nearly gets them all killed.
Failing to understand the very real frustration of Izzy Hands in this situation honestly seems like a lack of life experience—particularly functioning on teams with a lot of creative vision and low attention to detail.
Attention to detail isn't fun. It's boring, time consuming and often a slog. However, it's clear that Edward and Izzy made a good pair because Edward had the creativity to come up with outlandish, off the wall, genius ideas that made him an incredible captain—and Izzy could play the exact role of first mate, cleaning up the details, being the asshole that got the crew to work, and ultimately executing the plan put forward by the person with the vision.
(This is also why Izzy is so bad at taking on direct leadership—the skillsets overlap, but ultimately being Captain requires skills he doesn't have, and skills that are contradictory to being an effective First Mate.)
