Yes, vulnerabilities will always be found in every browser (it's practically impossible to make invulnerable browser) but IE is especially insecure because it's part of Windows and I don't think that Edge will be different. Microsoft is known for slow patching rate, it releases patches only once per month so hackers have plenty of time to exploit unfixed vulnerabilities.
First, I'll get you on the first point. The browser being part of Windows or not does not equate insecurity as it doesn't really matter if it's part of it. If there's a vulnerability in the browser, it's a vulnerability in the browser. Most Internet Explorer bugs are rightfully contained within Internet Explorer, or rather its layout engine - Internet Explorer's "integration" isn't that much of a big deal. You should think of Internet Explorer as more of a "shell" for the HTML rendering engine that's included with Windows, really.
Vulnerability disclosure and patching does not work the way you imagine they should, too.
Pretty much every single browser that you and I'd actually use operates on a set updating schedule, with out-of-band updates only appearing to fix critical issues, security or not. Microsoft adopts a Patch Tuesday - that way, every second Tuesday of a month, things get patched en masse. It's a much more convenient approach to patching, really, by keeping the "patch day" confined to known quantities under most circumstances.
You might have also noticed that the "normal" releases of Google Chrome and Mozilla Firefox also follows a set update schedule - after a certain amount of weeks, the browser will be updated, along with any new fixes. In a nutshell, all three are similar in update cadence.
In fact, rapid-fire updates tend to ruin things, as updates should ideally be well-tested before deployment, and firing off updates as the come in is a recipe for disaster in system uptime and usability. You also wouldn't want to have an unpredictable update schedule, too, especially in enterprise and mission-critical environments.
Hence, I do not see where your point lies, as it doesn't exist.
