The author seems to be claiming that beyond the outer walls castles don't have defensive elements as they are pointless once the walls have been breached. This claim is false.
> Sieges often didn’t involve much fighting at all, as simply waiting outside the castle till the people inside ran out of water and food was a much easier and less bloody way to win. In many cases simply realising the enemy was going to sit outside and wait was enough to surrender.
This part for example is just straight up false. While many more sieges were won by surrender than successful assault, sieges were very violent and full of fighting. Sallies and even open field combat between groups of warriors wanting to make a name for themselves were a daily occurrence. The vast majority of cities and castles under siege had plentiful water supplies and could hold up to a years supply of food under rationing, especially if they had any time to prepare for the siege (which they almost always did because moving big armies is hard to do discretely). That preparation also stripped the surrounding area of forage for the armies, giving them hard time limits on how long they could siege before morale cratered. The attackers were just as likely to starve unless they had a constant supply line which the defenders constantly tried to disrupt.
In order to overcome that disadvantage the sieging army had to really do a lot of damage and scare the besieged into surrender. Constant volleys from siege equipment into and over the walls, attempted escalades, towers and projectiles, and soldiers with pickaxes batter the walls. At the siege of Lisbon in 1147, two shifts of 100 men each shot thousands of stones a day using two trebuchets.
Major assaults would even be planned out in the open to drive fear into the defenders and try to get them to surrender before a large wave of violence.
Source: see the Soldiers’ Lives Through History - The Middle Ages chapter 4: Sieges. Lots of primary sources like the St Omer Chronicle in the notes.
I do remember that the first phase of the Punic Wars was basically Sparta chasing all the Athenians inside the city where they brought in supplies by boat and waited the Spartans out, rinse and repeat for a decade. Obviously that’s a different period and the Athenians suffered a horrible outbreak of some sort of plague possibly due to the overcrowding.
That comes down to the location and type of castle, nothing to do with period.
https://en.wikipedia.org/wiki/Caernarfon_Castle
has town walls, water on three sides, multiple independant keeps separated by curtain walls, etc. Once attackers "gained entry" they were faced with being in an enclosed space, surrounded by high archers, and tasked with as much work again to advance further ... only to be faced with the same again.
It was damn near impossible to siege as restocking from the sea and|or river was almost always an option at the time.
It was also a castle with decades of resources and cash thrown its way, other castles of the same period didn't fare nearly as well.
A great many of the Irish castles of the Ulster plantation and onwards fell to undermining - Irish sappers dug tunnels and propped the undersides of the walls .. only to later burn out all the props and collapse the walls.
There were only so many castles that had water access, multiple layered defences and granite foundations all about that resisted tunnelling.
Fred Dibnah included it in his programme on castles and how they were built. He also goes over its defensive and offensive features in detail.
Here it is on YT: