Per the article, G2A claims only ~1% of transactions on their site have problems like that. So assuming they're not lying, it's no surprise that you haven't lost any titles yet.
Also, they have no way to check the status of the keys. So, if a user doesn't report an issue, they'll never know about it. Given that the article says that most users don't notice keys being revoked, it wouldn't be surprising at all if the majority of issues never get reported.
Every time that's happened to me (for example, a time-limited version of a game or a beta), Steam presents a notification that the game has been removed from my library.
https://content.invisioncic.com/r273030/monthly_2017_05/Unti...
Are you basing this off the recent stunt they tried to pull getting people to publish favorable articles for them?
That was unacceptable of course but also I see why they are desperate to improve their reputation given the recent smear campaign against them.
Do you have examples of other instances where they were shown to be dishonest?
A bunch of esports teams dropped them as sponsors years ago after realizing they not an honest business. Their buyer protection service (G2A shield) is a scam. There's also this fun AMA they did https://www.reddit.com/r/IAmA/comments/5rg9mo/we_work_for_g2...
There's more here: https://www.reddit.com/r/pcmasterrace/wiki/keyresellers