I wish I could send invoices from my office without having to split pdfs in to chunks due to download size limits. It almost as ridiculous as having a fax machine in 2019.
I believe the main reason that there is a 10mbit limit is that if it's much higher then you have two consequences:
1) Mail in transit (and queue buffers) are going to be very heavy
2) Inbound mail being very large could cause you to exceed your storage limit and hamper the deliverability.
Point 2 is mostly mitigated now with the advent of cheap as chips storage, but point 1 is going to hurt mail relays.
As a sender, when you select a file from Drive, it defaults to sending a link, but you can change it to send as a normal attachment.
As a receiver, I believe you will see a Google Drive link, not a normal attachment.
I once worked on an app on phones that used libjpeg because te built-in 'hardware assisted' jpeg encoder was so bad. The typical photo was 5MB and simply reencoding it with libjpeg defaults resulted in under 1MB.
A simple bit of command-line magic can typically shrink those images massively before you email them onward.