The tasks in the tournament were dangerous because they were seeking to find the ultimate champion. Part of what makes a champion is their bravery in the face of danger, and ability to react and adapt their strategies. The champion therefore needs to feel there is a danger in every task.
What made it dangerous was the events of that particular tournament, mainly the first tasks.
In tournament of 1994, the first task was dangerous. Handling a dragon is not easy. It requires 8–10 fully grown wizard to stupefy a dragon. And even more dangerous it was due to overprotective mother dragons. So, involving XXXXX category beasts( the magical creatures which are impossible to train) like dragons was not a good choice. This first task tests their nerve by (theoretically) keeping the task a secret, so facing the fear of the unknown. They then needed to think on their feet, and the danger was directed at themselves. How does an immediate threat (a protective dragon) affect their ability to complete a challenge? In the book, this danger is limited because the dragon isn’t able to break free of the enclosure. The Harry vs dragon movie fight was (unnecessarily) added for Drama.
However, the second phase was not dangerous. And merepeople are actually not aggressive like shown in movies. They just don't want to interact with wizarding world too much cuz, y'know, humans are scumbags. Giant squib of Black lake is not dangerous too. I mean as it saved Young Creevey after he fall into black lake. And grindylows are not too dangerous as Prof. Lupin was having a tank full of them and he taught third year about them. It was in DADA exam too. So, second task was not that difficult. It was just searching for ways to survive under water for one hour and recover your friend.
Thus, the second task takes that further because the apparent danger is directed at someone else, and someone the champion loves very much. This task also involves intelligence in working our the egg clue, and then strategizing in the face of an impossible task (breathing underwater) within a time limit (1 hour). How does the threat to their loved one affect their ability to think clearly?
However it’s important to note the threat in this task is not real:
The mermaid song informs the champions that they only have an hour to rescue their treasured possession, and after that it’s too late.
We know that the “hostages” were taken to Dumbledore’s office where he clearly explained the situation to them. They were put into an enchanted sleep and told they would wake up once they were above the water. If they hadn’t been rescued, the merpeople would have brought them up to the surface. Dumbledore assured the hostages that they were in no real danger at all.
This is why Ron and Hermione are exasperated with Harry because he refused to leave anyone behind. They tell him he should have just taken Ron and left, which would have won him first place (as he reached the hostages first out of all the champions). Ron tells him he was an idiot to take the song seriously, and points out none of them would have drowned if their champion had failed.
There is a big difference between this task in the books and in the movies. The creatures in the lake aren’t a big problem and Harry doesn’t almost drown because of Grindylows. It’s very clear it’s the time pressure, and not knowing where the merpeople village is that is the stress of the task. When Harry reaches it, his worry becomes about the fate of the hostages once the hour has passed.
Third task was a bit difficult compared to second task. (Excluding Barty Crouch Jr. and Voldemort's involvement in it). The task was to search for the triwizard cup which was a portkey. A lot of obstacles were there like boggart, sphinx, blast ended skrewts, etc. The only dangerous beast was Acromentula (become of their venomous pincers).
So, the third and final task is different yet again. They are told what the task is (get to the cup), and that the obstacles will be creatures and enchantments. Their goal is a relatively simple one. This task tests their repertoire - how can they adapt to a range of situations? Some are intellectual challenges, some physical. There is an element of being able to prepare, so how do they use their time before a challenge they know is coming? Equally this task is a direct race with the other champions, which adds a new element - it’s not supposed to be dangerous, more like testing their competitive ability. Again there is a big difference between the book maze and the movie maze.
Sooo apart from the dragon task, over all, not that dangerous imo.