The way you have your system setup is the same way I have mine, with no issues. 

What kind of problems are you having? 

Do you have the Arc’s WIFI enabled? This is how the Sub and surround bond with the Arc.

Can you provide more information about your network?

I unwired my Arc and have my system fully on my wifi and find that works best here.

You may want to try that and see if it improves things.

Next would be waiting for a problem then submitting a diagnostic and calling Sonos.

My last option would be  buying Ethernet connectors for the 300s and wiring everything. Save your money and wiring effort unless it is needed.

Cracking from all speakers, the subwoofer is non existent frequently, drop outs. Tried power resets, factory resets, resetting router, trueplay again etc. Also i feel large parts of the soundtrack of movies is missing with background sound being extremely quiet and dialogue being very loud.

Stop the factory resets, they aren't going to help.

They will erase diagnostics data support could access to evaluate your problem.

But that is the suggestion of Sonos Support!

You sort of failed to mention that.

As the support documents say, after consulting support, is one of the few times you should do a reset as they have had a chance to collect the information that is lost.

What i want to know is is a fully wired home theatre system with disabled wifi for all possible? will the speakers communicate through ethernet then instead of wifi?

Your surrounds and sub communicate with the Arc via a dedicated 5ghz WiFi to keep them all in sync - wiring them won’t help. 
I have an Arc, sub and surrounds, and none are wired. I have assigned each speaker a fixed/static IP address in the router’s DHCP setting which really helps with stability. (You would then need to reboot the router uoff for five mins] and each speaker, at the wall, if you want to try that route.)

Yes, it is possible. Not suggested, in my mind, you’ve paid Sonos for a lot of hardware that you’re not using, why not go with a true wired speaker system, instead of one connected by Ethernet? Less chance of delays from your router, for one thing. But yes, all will communicate through Ethernet to your router. 

But Sonos is first and foremost designed to be wirelessly connected. That’s what Sonos is ‘about’.