For sure, but everything is relative. Ignoring for a second the lock-in factor of using a @gmail.com address, I would trust Google's MX servers any day over Gandi's, especially after this last incident (trust == reliability in this context).
Google's MXes are notoriously strict and drop or permanently delay emails all the time for reasons beyond your control as a recipient
an example from 5 minutes ago from one of my MX'es (which only forwards, after heavy greylisting and spam filtering):
Jan 9 18:05:59 mail postfix/smtp[26197]: to=<ABC@gmail.com>, orig_to=<XYZ>, relay=alt1.gmail-smtp-in.l.google.com[209.85.233.26]:25, delay=25000, delays=25000/0.01/1.6/0.16, dsn=4.7.0, status=deferred (host alt1.gmail-smtp-in.l.google.com[209.85.233.26] said: 421-4.7.0 Our system has detected that this message is 421-4.7.0 suspicious due to the very low reputation of the sending domain. To 421-4.7.0 best protect our users from spam, the message has been blocked. 421-4.7.0 Please visit 421 4.7.0 https://support.google.com/mail/answer/188131 for more information. ABC - gsmtp (in reply to end of DATA command))
that's not my reputation (which is high), that's the reputation of the sender's From address
and it doesn't send it to the spam folder, it just delays the email forever until my MX gives up
Interesting. Would you be of the opinion that sending mail from my personal @gmail.com address would then have much higher chances of being successfully delivered to other people (most of which will inevitably be at another @gmail.com address) than those sent from my "portable" @custom.domain address?
unless you run all the MXes (and can prove otherwise): you're likely having emails dropped all the time already