This is the reality of nearly all Android devices. This is an Android problem in general, not just a Samsung problem. Samsung certainly doesn't help themselves by being one of the slower OEMs at updating (Motorola, Sony, even HTC can school them, for sure), but this should be nothing new to people familiar with how updates work on the Android side of things.
Here's my take, and most will have heard this already. And this isn't necessarily directed at you, as I'm sure you've heard me say some of these things already, too, and/or know of them yourself. Just saying in general:
1) Nexus owners don't necessarily get updates on the first day either. Even current generation Nexus device owners may have to wait weeks because Google rolls them out in waves. They do this to prevent major issues (like the one that bricked iPhone owners last year). Of course, weeks is still better than months.
2) Stock Android is, for some (myself included), too stock. I'm not willing to sacrifice day to day useful features for a quicker update. I rather have, say, TouchWiz on my device and benefit from the extra features and tweaks that make my daily smartphone experience better and easier.
3) Ditto hardware. Nexus devices don't always offer the best hardware. With, for example, Samsung, I get hardware features and benefits that translate to daily gains. With the S7 in particular: leading class screen, battery size, and camera; waterproofing; expandable microSD; design and ergonomics. Etc.
4) Most Android OEMs and carriers are pushing out those monthly security updates. Samsung just pushed out February's a few day's ago. They may not be exactly monthly and/or certain carriers may push them out slower after the fact (Tmobile hasn't been bad actually. I got the January one in early February, I want to say? If my memory serves me correctly). Also, your device in general is pretty protected already by the sheer fact that most (if not all?) malware/virus requires user approval to get onto your phone to wreak any sort of havoc. The best security feature is common sense. Only install from the Play Store. Avoid unknown sources/app installations. Don't click on weird links from suspicious email or unknown texts.
5) Google updates their core apps. And if you're heavily invested in Google (Gmail, calendar, Hangouts, keyboard, Google Now Launcher, etc.) you'll find these updates are actually quite frequent.
6) The extra long wait is usually due to approvals and quality control. And this leads to safer and more bug-free updates. Does it take half a year to QC an update? Heck no. For this point, I'm merely pointing out the silver lining.
7) Another silver lining: It's worth noting that today's Android that ships with most modern day smartphones is a stable, fast, reliable, and secure OS. Software updates back in the earlier years of Android mattered so much more because Android still had so much work to do and room to grow. That simply isn't as true these days; the differences aren't as great.
Again, these are just my thoughts and experiences. If one truly values timely software updates, Apple and Google Nexus are definitely the way to go. To me, it's not a deal breaker. Far from it. Updates are fully welcomed, but slow updates just aren't as important to me after you factor in everything else.