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It's not an "incompatibility with Akeeba Backup", it's how the operating system works. Every time you need to write to a file in PHP, PHP has to tell the operating system to go to a specific location of the file and append some data. These operations take a couple of milliseconds on a local file system. When you are using NFS (Network File Shares) each of these commands has to go to the operating system's TCP/IP stack, wait its turn (after the server is done satisfying packages of pending web requests), get transmitted over the NIC (network interface card), reach the other server's NIC, wait for their turn, get processed by the other server, perform the filesystem action, prepare a reply and follow the inverse procedure to send it.

If it sounds like an extremely complicated way to do that, it is. Using NFS shares is dead slow. It's also dead cheap, since there are devices you can cram with dozens of disks and put them on the network as one, big NFS share. As a result this is used a lot for cheap, low quality, shared hosting. The sites will be much slower, but who cares if the client can pay peanuts to get it?

So, the best way to increase backup speed is to use a decent server. Using a decent server means increase of cost: a decent shared server starts at about 80 Euros per year. As a result you have to weigh two things: does it make more sense to have a fast backup or more money in your pocket? The backup can be automated (scheduled) so it doesn't really matter if it takes 20 seconds or 20 minutes. On the other hand money doesn't grow on trees. This dilemma is yours to answer.