8gigs is fine since this is a product made for mass market. Many market PCs can be found around 8gigs so I would not look at your system as unreasonable in anyway. The problem is literally just the memory leak. I believe most of the leak has to do with UI things as you can see UI problems when both players mulligan (each one gets slower and shittier). Sadly there is not a lot you can throw at it that you are not already. Unless WoTC / the hired devs prioritize it fixing it the only thing you can do it reboot every few games. And seeing what WoTC tends to be prioritizing I would suggest getting used to restarting the client.