Why are attachments so damn slow to download compared to Gmail?

I am on EmClient 9 Pro and I often need to login into the Gmail web browser interface just to download attachments because downloads through EmClient are ridiculously slow.

Today I tried to download a 900kb PDF and it took 20 seconds.
The same attachment through Gmail web client < 0.5s.

I am on a 200MBps fibre line and don’t have issues with any other software or services like this.

I have seen others post here about this, but no response from support, even for Pro customers, which is disappointing.
Please advise.