highest and lowest in aftermarket seems extreme?

For every trade that occurs, there is a buyer and a seller. Ignoring special circumstances like the seller just needs the money, one of these traders is wrong.

Your premise is that the lowest price might be real because everybody tends to buy lower. I'd ask you this in return. The market is up 50% in 9 months and is it trading at record highs. Why is anyone buying anything? The answer is that many believe that the market is going higher. They may be right, they may be wrong but either way, they are expressing their outlook with their dollars.

As to your question about the pre- and post market, that's a bit of a different beast. It tends to be illiquid with much wider spreads and because of reduced volume, it is more volatile. It takes far fewer shares to move price after hours and that is reflected in wider price swings. With many stocks, that same share volume that moved after hours price would likely be swallowed during the regular trading session, barely moving price, if at all. And to a lesser extent, sometimes, that crazy price is just that, caused by a fat fingered trade and sometimes it's just bad data.

A word of caution: Do not trade during after hours unless you are an experienced, decisive trader. The exception to this would be if you are either closing or hedging an existing position at a good price.

There is always a buyer at the highest price and a seller at the lowest price. It isn't necessarily bad, though. The seller at the lowest price could have bought a year ago at an even lower price. The buyer at the high price may expect that the stock will continue to grow and not be concerned with the entry price. If you had bought Amazon at the "high" price for a day 5 years ago (somewhere round 670), you'd still have about a 400% return.

Buy-and-hold investors shouldn't worry about daily fluctuations - they are looking for long term growth. Only day traders stress over the daily high/low.

There's much less trade volume after hours, and low volume (almost?) always means higher volatility.

This is what you see.