You (and Carlin) have a post-Vietnam interpretation of "shell shock", made possible only because of the success of PTSD for classifying and treating emotional injuries.
We can look to the post-WWI era 'Report of the War Office Committee of Enquiry into "Shell-shock"' to see how in 1922 they viewed "shell shock" as a congenital or upbringing failing. From https://archive.org/details/b3217777x/page/96/mode/2up?q=con...
> Authorities are agreed that, in the majority of cases of war neurosis, there already existed a congenital or acquired predisposition to pathological reaction in the individual concerned, and that this constitutional characteristic was of vast importance.
We can see how many viewed it as simple lack of morale:
> Major Adie tritely expressed himself in stating that there was only one word worth mentioning, and that was “ Morale.’’ If you keep up the morale there will be no “ shell-shock.’’ The medical officer should know his. men, and can prevent the vast majority of nervous cases—mild “ shell-shock ’’—from becoming ‘‘shell-shocks’’ by retaining them at the front, or by giving them a little rest at the front. As long as they were living with soldiers, and in the atmosphere of the front line, the tendency was to recover. They were to be looked on merely as physically exhausted. - https://archive.org/details/b3217777x/page/158/mode/2up?q=mo...
> He agreed with the regimental opinion that a large number of ‘‘shell shock’’ cases in a battalion may be taken as a sign of poor morale. - https://archive.org/details/b3217777x/page/16/mode/2up?q=mor...
Then there's the difficulty of figuring out if someone is suffering from shell shock or is a coward - the latter being punishable by death:
> Asked whether he had any experience of cases of men charged with certain military offences, such as desertion, in which the plea of "shell shock" was put forward, the doctor said he saw many such cases. As Neurologist of the 4th Army, all cases which put in a plea of "shell shock" as an excuse for desertion were sent to him for medical examination and report, and he was always asked to give evidence in courts-martial on these cases. He confessed it was an extremely difficult and distasteful task, and he very soon came to the conclusion that it was almost impossible for the Medical Officer to make a decisive statement ... - https://archive.org/details/b3217777x/page/42/mode/2up?q=exc...
Or if someone is shirking duties by claiming shell shock:
> "Shell-shock" became recognized as a handy excuse, and, indeed, a suggestion also to the many who were ready to avail themselves of any subterfuge to escape from the terrors of the front. - https://archive.org/details/b3217777x/page/140/mode/2up?q=ex...
As a result, the British government decided "that quasi-medical words like ’shell-shock’ should never be used, that the whole question of psychoneuroses should be both recognized and played down, and that no pensions should be paid." (quoting https://journals.sagepub.com/doi/abs/10.1177/0957154x9901004... ).
The term "shell shock" was not used in WWII. From the last source, "’Not Yet Diagnosed (Nervous)’ (NYDN) or ’Exhaustion’ being the commonest. The troops had a variety of terms, notably ’Bomb Happy’ or ‘Windy’."
So no, it wouldn't have been more difficult. It was viewed as a moral or congenital failure of the solider to carry out his service.