In theory, that all looks good. In praxis it is a fact, that i.e. my Nexus 5 (but also my work Samsung S5) stutters and lags a lot sometimes. After deleting the app cache, the problem is solved most of the times.
...<snip>.... and I found out it is good practice to format the cache partition after an OTA update.
When you say "Delete app cache" - what exactly are you doing? Are you killing the running processes? Or are you going to settings/storage and deleting the "cached data"? Deleting the cached data is not going to improve your phone's performance, unless you are running really low on storage space.
Killing the running processes MAY temporarily make your phone seem "snappier" - because if your RAM is all filled up with running/cached processes (which in itself it not a bad thing), you are basically forcing all processes to be killed, instead of letting Android OS do its thing and swap processes in/out.
The only reason why it may make your phone seem temporarily snappier by killing processes is because of a memory leak that existed till one of the recent builds (I believe it existed even in the initial Marshmallow build). The reason I say temporarily is because those background processes that you killed will be resurrected by themselves pretty soon. And furthermore, when you launch an app that you killed, it will take slightly longer to launch (because it is no longer in RAM), and will consequently result in a slight increase in battery drain as well.
Wiping the cache partition after an update is a different thing - that forces the OS to rebuild the cache partition - I highly recommend that as well, so that it rebuilds based on latest files, rather than just based on updated files.
As you are telling me about your Smartphone knowledge, rest assured, I am an old timer when it comes to PDAs and smartphones. I had my first Palm PDA in 1994 and since had most brands at least once. I also had most of the Treos as well as a Pre+ and a Pre3 as well as a HP Touchpad. I was one of the first here in Austria to have an XDA Smartphone with Windows Mobile on it. I had two iPhones and the Nexus 5 is my third Android smartphone.
So yes. I know a little bit about the matter. Thanks.
Please understand that Android OS works VERY differently than Palm/WinMo/WebOS/iOS. I've used all of these as well, and with these, if I didn't kill the running apps, my phone would grind to a halt (well, except iOS, which would pretty much kill the app itself when I exited it).
I still have my N5 in the family (I moved to a N6). Yes, on my N6, the recents menu becomes cluttered after a while, and every now and then, I do go and clear it out (not because of any performance issues, but because it is hard to find what I need). But on the N5, the recents menu is never cleared (annoys me if I ever pick it up) - family just doesn't care about it - because it doesn't impact performance at all.
The recents menu is just showing you a thumbnail of the app. Android may have already cached the app itself, or killed the app if OS/apps needed memory - the entry for the app still remains in the recents menu. Swiping it away isn't freeing up any memory in that case.
To add to what Crashdamage said - if your Nexus 5 is getting slugging/laggy after a while, you should try to figure out the cause for that problem itself. What build are you on? Are you using a stock ROM? or a custom ROM? Have you ever performed a factory reset? Do you ever flash factory images? Or do you always take OTA?
Regarding apps - Hangouts, Gmail, Chrome, Google Now aren't going to cause laggy behavior (facebook - I don't know - I don't use that app - have heard that it causes wakelocks for some folks etc - perhaps).
Go to settings/memory and look at memory usage. How much is free? While you are there, tap on "Memory used by apps " and see what is hogging up your memory.
Edit: Your Samsung S5 - whole different animal. What I wrote above applies to your Nexus device - may not apply to your Samsung S5 - they alter the memory management (more aggressively kills active apps I believe, because touchwiz and their other apps take up so much of available memory)