The solution is to use the appropriate tool for the job. If you're locked in to highly crusty legacy software, it's inevitably going to require workarounds. There are good technical reasons why arbitrary-size single-part file uploads are now considered an anti-pattern. If you must support them, then don't be shocked if you wind up needing EC2 or other lower-level service as a point of ingress into your otherwise-serverless ecosystem.
If we want to treat the architectural peculiarities of GP's stack as an indictment of serverless in general, then we could just as well point to the limitations of running LAMP on a single machine as an indictment of servers in general (which obviously would be silly, since LAMP is still useful for some applications, as are bare metal servers).
If we want to treat the architectural peculiarities of GP's stack as an indictment of serverless in general, then we could just as well point to the limitations of running LAMP on a single machine as an indictment of servers in general (which obviously would be silly, since LAMP is still useful for some applications, as are bare metal servers).