On one hand, Hamilton was nowhere near the apex and never was in front of Max, so he was out of position trying to stick a wheel in there on a 150 mph corner, but on the other hand they were so incredibly close and things happen in racing.
Verstappen was ahead + he gave Lewis plenty of room to take the inside line of the corner. That was 100% Lewis' fault.
The FIA defines being "significantly alongside" as having your front wheel at the very least lined up with the rear wheel of the car in front, in the braking zone, as both cars are committing to their lines. In this purely regulatory sense, Hamilton did nothing wrong. It doesn't matter that he wasn't fully ahead of Max before the apex -- not every overtake is accomplished under braking before the apex.
However, situationally, Hamilton really should have known better. That's a super dangerous corner to do what he did. In fact, nearly all the veteran racers on the broadcast immediately said "oh no, oh dear no, you don't do that going into Copse... you could seriously hurt someone". Hamilton let desperation take over for a split second and he punted Max off the track.
Y'all are right, it should have been a drive-through penalty to be served within three laps. If that had been the case, Hamilton would've immediately slipped to P7 or P8 and winning the race would've been much more difficult for him and the team. But instead, we all saw the joke that happened.