While the technology you describe might have been in use 50 years ago, it's definitely not used today.
Modern electrolytic caps DO NOT use paper, and they ARE sealed.
This is a pointless discussion since the recommendations of the manufacturers are clearly stated.
Capacitors in photographic flash units behave quite differently than those in regular equipment because they sit unpowered
for extended periods of time, then are expected to operate as low-impedance sources intermittently.