As‘salaamu alaikum, brother. After reading and pondering your question, I am left with the impression that you misunderstand the full scope of the jihad bin‘nafs. I say that because of your statement: “How can self- control be a greater jihad than participating in war, where you have to withstand real physical hardship and risk your life and spend your wealth? It is illogical.”
Yes, self-control (sabr) is an important part of the jihad bin‘nafs, but it is by no means the whole of it. The ultimate goal of the jihad bin‘nafs is “taz‘kiah” (purification and beautification of the soul), and that is where the weightiness of the jihad bin‘nafs becomes obvious because taz‘kiah has direct bearing on our success or failure on the Day of Judgment.
Consider ayah 7 - 10 of surat-ush-shams (91):
“by the soul, and the proportion and order given to it, and its enlightenment as to its wrong and its right. CERTAINLY, HE SHALL SUCCEED WHO PURIFIES IT, AND
HE SHALL FAIL WHO CORRUPTS IT.”
Consider also ayah 15 - 18 surat-un-nazi‘at (79):
“Has the story of Musa reached you? Behold, your Lord called him in the sacred valley of Tuwa: ‘You go to Fir‘awn, for he has indeed transgressed all bounds. And say to him - would you (like) that you should be PURIFIED?‘”
The jihad bin‘nafs is THE WORK that must be done to achieve taz‘kiah. And it is indeed an intense struggle, especially in the world we live in today. But lets look at some simple aspects of it.
A war is not the only aspect of jihad fee sabeelillah. Building masaajid, schools, and hospitals is jihad fee sabeelillah too. So is clothing the naked, feeding the hungry, and providing shelter to the homeless. Overcoming our stinginess to give our wealth to finance these causes is jihad bin‘nafs, (64: 16).
Dhikr to Allah is Islamic meditation. Do you know how much we are supposed to do it? CONSTANTLY! (7: 205; 33: 41 - 42; 73: 7 - 8; 24: 36 - 38). But we live in a time of constant distraction AND TEMPTATION (but that‘s a whole new discussion!). Anyway, remembering our Lord in a world that is doing its best to forget Him is jihad bin‘nafs too.
How is the jihad bin‘nafs greater than jihad of war? Because it is the jihad of striving to achieve salvation for ourselves in the akhirah, inch by inch and day by day. It is constant and unrelenting. There are no days off from the jihad bin‘nafs.
That is my understanding of the matter, but Allah knows best. Ma‘as‘salaam, brother.