This is to be expected and is working as designed. Sonos speakers not part of a home theatre system, create a buffer to enable multiple speakers to play the same music in sync.  

In Settings/System/<Arc_room>/Group Audio Delay you can adjust the buffer size for TV audio playback in the grouped speakers. 75ms would however still be obvious if the grouped ‘rooms’ are in the same physical space as the Arc.

The delay on the Roam is substantial so I don’t think any of the settings being changed would make any difference. 
 

It would be a shame if it’s designed to be like this as @UKMedia has suggested. Why would there not be a way of syncing all within one group?

There is no buffer involved when the only device is a Home Theatre set-up as there would be lip sync issues.  But when other Sonos units in addition to the Home Theatre unit are grouped together then a buffer is used to ensure that all  devices play in sync.  For Music this is not recognisable but with TV output, the delay you are getting is the result.

Well, there still is, but it can be made smaller due to the network architecture. 

Ok maybe I will give up trying to make it work and just stick to the home theatre set up I have and not try to over complicate it. 
 

Thank you everyone for your help and time. 

It’s one setting!  Maybe 4 clicks in all.  You aren’t even going to try it? 

And as far as the reason why it’s delayed for TV sources?  Physics.  I’m afraid you can’t fight physics.