Tyrants are strong and tough, but they are so huge that any attack on the base, as long as its defended, will likely kill them, they are such a huge target so attract a lot more damage and can not escape as easily because they can not jump and get boxed in because again, they are a huge target, maybe if their trample damage was always on without the speed boost it would prevent them getting boxed in, 5 tons should be able to walk right over a human.
In open human bases this is not as much of a problem but with more compact ones you see alot of tyrants circling outside untill they can build up points before they suicide rush, as it will inevitably be as aliens behind them or humans will trap them.