Avast is not heavy. It is quite a light antivirus, even with all its various components. I have been using Avast since many years now. I am now using it on my Windows 10 32-bit desktop with 2 GB RAM, and Avast doesn't slow down the system at all.
I should say though, that I only use the file shield, web shield, and behavior shield of Avast only, and I disable rest of the components during installation, because this is all is needed.
The culprit must be something else. As someone said in a post, that the reason for hard drive being thrashed is that the RAM is being used a lot, which results in the computer using the memory swap area, which is on the hard drive. So, you need to find out what is using the memory so much.
You can use Firefox, if you feel that Google Chrome is using a lot of memory. Chrome uses a lot of memory, if you tend to open a lot of tabs. For the same amount of tabs, Firefox uses lesser memory.
Have you run scans with Avast and Malwarebytes Anti-malware on your computer? If not, I suggest that you run scans, and ensure that the thrashing isn't because of a malware problem. Sometimes, it can be a cause.
When did this issue start happening, do you remember? Do you remember if it started after you installed any new software or something?
Try to see which process is using up the RAM. That might give you an indication.
Do you use Windows apps? By that I mean the apps, that you download from the store, and not the usual desktop software that we install and use. Did you uninstall all the unnecessary apps that came by default with Windows 10? These can often run in background and cause RAM to be used.
You should spend sometime tweaking the Windows system to disable or uninstall all the unnecessary components. Try disabling or removing unnecessary start-up items. Remove unnecessary Windows components from Programs and Features.
If all this fails, then I suggest that you do a format and reinstall of the OS, if you can. Do backup your important data before you do that.
I noticed earlier in one of the screenshots that you were using Spybot on your computer. It is an old software, which isn't effective anymore. Please uninstall it. You should install Malwarebytes Antimalware free version, which is a far better software now, and you should run it on demand, means, only when you need to scan the system. Disable it from starting up with Windows. In free version, there is no real time monitoring anyways.
So, remove all such unnecessary software, like Spybot.