I replaced my Arc and Play 1 surrounds with an Arc Ultra and a pair of 300s, keeping my old full Sub.

I find the improvement worth the money although I ended up replacing the 300s with 100s due to the locations I had available long term. The 300s were noticeably better on Atmos content but I find the 100s acceptable. 

Thanks Stanley for response I do think the Sonos arc ultra will be a purchase it’s just the rears I need to decide on. Thanks for advice

If you can set them up decently you won't regret the 300s.

I moved my 300s to a different room and am using them as an Atmos pair and they sound amazing.

I would probably look into upgrading the sub mini to a full sub though, depending on the size of the room.  Since you are using an Arc, I’m assuming this is a larger room that could benefit from the additional bass volume.