This is essentially saying that all goaltenders are identical, and play at the exact same consistency and ability at all times. We know this is not true.
Yes, defensive metrics of the team in front impact goaltending, but those don't vary between teams by nearly as much as people think. The play of the goaltender has a much bigger impact on the resulting GA. We have the information to know how much the goalie and team in front each played into the resulting GA stats, but for some reason, you're choosing to ignore it.
The Islanders weren't horrible defensively last year. They also weren't near the best, and have gotten worse this year. This all started with a statement that the Islanders goalies have so much more help in front this year, absolving Andersen of blame. This is not true. In reality, Leafs and Islanders aren't all that different in defensive results this year.
It's weird how adamantly some deny the impact of goaltending, while at the same time claiming that Andersen has carried league worst defense for years, and demanding a trade for a backup.