From the photos I would say, that looks like an expensive high quality expedition ruck sack which now a days costs new from European production round about 500 €.
Should it be uncomfortable, you could ask in this forum which modern carrying system would fit. Savotta and Tatonka sell similar stuff for example, a larger community plays around with old similar looking Swedish army rucksacks.
I guess if you replace the hip belt and carrying straps it will become more comfortable.
But I used a lot over many years and several thousand kilometers an archaic more than 100 years old swiss artillery Tornister which fits perfectly to me and which is in my opinion absolutely comfortable how it is. I just added an old Bundeswehr padding to my swiss carrying leather straps which looks more or less like the carrying strap padding at your photos. And I used another German BGS Rucksack with wide leather carrying straps which is comfortable how it is.
What I want to say: If it's comfortable or not depends mainly on the right fit and correct adjustment, not on the thickness of the padding in my opinion.
And of course mainly the weight one throws in it is the reason if a hike is a fun or a torture.
