Actually, it can use 16GB of the "correct" type, I use that in one of mine that is beeing used for various taskes.
For a "storage only" NAS, based on the G7 series, even 4GB is allmost "overkill".
But if you use it for Plex, and need CPU based transcoding, well...then there are better choices as you have noticed
When I was getting my first demonstration of the G7 (N36L) when it came out, I "fell in love"
Back in 2010 (?) this small package came with a big usefullness, and when it later on was getting updated to the N40L and the N54L
the size and handiness was perfect for small offices and home usage.
If I recall correct, the first N54L I was buying for my self, (2014?)
came with 4GB RAM and a 250GB drive, for a price of about $150,- USD That was Bang for the Bucks!
Now, even if it's dated, it plays a nice role for my usage, 5*4TB WD Red + SSD readcache, as (among other things) datastorage for my ESXi host.
As mentioned above, ther is now driversupport for the internal nic if you go DSM 6.2.x, but it can be "tricky" as you have to "patch" the USB stick.
And who knows if Synology relase another update that breaks the system, as when going from 6.2 to 6.2.2?
If you stay with DSM 6.1.x, it's more of a "plug and play", no need for extra drivers and to me it feels more "bullet-proof"
as I think it will only get security updates and no bigger changes, due to the age.