There are people who will try and carry-on everything for a dive trip. Personally I don't see how it's possible (while actually staying within the rules) and have no desire to try.
Lost luggage does happen but it's actually pretty unusual, and I think technology has improved the situation over the years. There are tons of existing threads on this subject with good information. And various ways to decrease your chance of issues. Some of this is location specific. No regulators in carry-on is a Philippines thing, not sure if it's an issue anywhere else. Non-US carriers usually have smaller size limits for carryons, and rather small weight limits for them that tend to get enforced. If you're on a small plane along the way you will probably need to check more for that flight and want to be prepared for it. OTOH, some carriers will give free or cheap allowance for a bag of dive gear. You have to figure out the best way to pack for each trip for you.
Pay attention to rules about different types of batteries. Cozumel it's illegal to take in Sudafed, much discussion about that here lately. There are different quirks for different destinations you should look into.