I know all of the Alonso fans are in a tizzy over this, but it was an appropriate penalty.

Everyone upset seems to be buying the line that he was taking the corner slower to get a better exit. That would be late apexing. When you do that, you brake LATER and turn into the corner LATER (at a sharper angle), then apply throttle EARLIER. Alonso's actions are inconsistent with an intent to get a better exit.

He broke earlier. Then he sped up. He entered the corner on the usual line with extra traction available. Then he jabbed the brakes mid corner. If he had taken the corner at normal speeds, that would have absolutely upset the car, so this was PLANNED. Immediately after jabbing the brakes he is back on throttle and accelerating out of the corner.

I believe his intention was to force Russel to react to his behavior, then accelerate away while Russell reacts to him braking, to build an extra bit of gap to neutralize the drs advantage.

This was absolutely a brake check. Alonso has done this many times before, and he usually gets away with it because it is on the line or he has a plausible excuse for his actions. This time he screwed up and took it over the line.

You know his intentions here because he was immediately on the radio making up an excuse for his actions. Except that excused didn't jive with the telemetry so he had to give the stewards a DIFFERENT excuse which still isn't plausible (see late apex above).

This penalty isn't punishing him for driving defensively. It won't result in drivers getting penalties for parking their car on the apex. This penalty was about erratic driving that compromises the safety of other cars and drivers on the track. The outcome here is direct evidence of the safety concern.

As much as you may not like Russel or question his skills, ask yourself what would have happened to other drivers in this situation? I would argue 2/3 of the other drivers would have bottled it the same way he did.