You can make a custom search in the replay vault to show only high-rated ladder games on a single map, such as Point of Reach or Roanoke Abyss. Just pick a minimum rating like 1600 or 1800.
If you want to watch older replays, you may need to disable your UI mods.
If you look over this you should see how often these players switch between different openings like transport first vs. making scouts and interceptors first vs. trying to use 1 or more bombers before making a transport. Another opening that you haven't mentioned is to make just a very small amount of scouts + interceptors first, like 1 scout + 2 interceptors, before the transport. The scout can look at their base, and you can see either there is a transport being made OR there are barely any engineers (meaning a transport already took them) OR they're spamming interceptors OR they're making bombers. Whatever you see, you can use that to decide what to do next.
Making 2 bombers does not ensure that an expansion is denied. Engineers can try to dodge, bombers can be shot down, and higher-rated players usually split engineers so that a bomber will need multiple passes.
It is something like "rock paper scissors." If you always make bombers, your opponent can counter that (two simple counters: 1 spam interceptors to win air and then use that to deny your transports, or 2 just have some interceptors with the transport to protect it, if they suicide to kill the bomber, they save the drop). So you need to be unpredictable. For the same reason, you don't always send a transport to the right (or to the left).
A drop doesn't need to survive very long to be safe from bombers. If you drop 4 engies, they can split (3 seconds), make a factory (15 seconds), and the factory can make a mobile aa (15 seconds). So basically 33 seconds after your drop happens, there is a factory + an aa, which means it would take a lot of bombers to kill the drop. Bombers might get good work done (kill 3 engineers, that would slow you down) but you have a factory to make more, so the drop itself is safe.
Another thing to consider is, if you're going to lose the transport, have it drop engineers before it gets shot down. Often they can walk the rest of the way, or make navy factories, or do something for you.
Also, if there is going to be an air fight around your transport, there are tricks you can use to keep it alive longer. If you pull it back in the opposite direction, enemy interceptors can fly past it and need a long time to loop around to shoot it again. That can give your interceptors more time to try to kill enemy interceptors.
Edit: also, when you are choosing replays to watch, a short replay indicates that one player's opening got crushed by the other player. A longer replay indicates that there was no crush. I think you would want to watch BOTH types of replays (at least, the first 7 minutes of them) in order to get a full picture of what typically happens.