the mandate being very wrong, but on the other hand it clearly says about the rights of existing people, which israel is clearly doing the opposite.
You've got it backwards. It is incontestable that Arab governments (starting with the illegal state of Jordan in 1921, long before Israel's independence war of 1947) have violated the Sevres provision by expelling their Jews and seizing Jews' property. There is a good argument that this releases Jews from respecting the same; nevertheless, Jews continued to obtain private property by purchase, not seizure from Arabs, appropriating only "state" (formerly Turkish) lands for themselves.
Your confusion is rooted in how this process was done. The proposal to evict Jews from Palestine via terrorism was first made by the Mufti of Jerusalem in 1899. The Turks rejected this. However, the religious imperative became a tool in the hands of the powerful to accuse other land-owning Muslims of impiety by accusing
them of planning to sell their lands to Jews. The "strong" Muslims (usually relatives of the Mufti or Arab-Ottoman officials) would then compel these weak Muslims to sell them their lands, which they in turn
they would sell to Jews at a 4000% profit. (Forty times the original purchase price.) So throughout the post-WWI period of Zionist settlement, land purchase and anti-Zionist propaganda went together.
During and after the 1947 war matters became even more garbled:
1) Hundreds of thousands of Arabs, including entire villages, following their own leaders' encouragement or example, abandoned their homes in Jewish Palestine. (Of all the refugees, perhaps only fifty thousand were expelled, those in the Lod area whose leaders, late in the war, reversed their previous pledges of peace to the Zionists, deciding that the compulsion of Arab terror directed against them was more compelling than Jewish threats.)
2) A special agency was created to care for or create Arab refugees and (unlike other refugees worldwide) coddle them in perpetuity. The legal grounding cited for this is the same League of Nations Mandate that establishes Israel, supposedly obligating the Mandate power (first Britain, then the U.N.) to care for the population in its territory.
3) Egypt and Jordan occupied large swaths of Palestine. Gazans were not treated as Egyptian citizens. Jordan annexed the West Bank (only Pakistan recognized this, with murderous results) but established a kind of second-class citizenship for its Arabs.
4) The Arabs remaining after the war was over kept their lands and property. Abandoned property and villages were built upon by Jews, save that the Arabs who fled were allowed to return conditional upon their swearing allegiance to the Jewish State. Israel is 20% Arab today.
Is that proof enough of Israel's good intent and faithfulness in following the will of Caliph Mehmed VI, who was so concerned about Jews not violating the civil rights of Arabs? The Arab states can say nothing about their own good faith in this matter, can they?
(You'll note the absence of Arab civilian casualties in this account? That's because there were very few. Everyone remembers the dozen or so Arab civilians murdered in the confusion of Deir Yassin. Hardly anyone recalls the Arab revenge attack a few days later, the murder of over seventy unarmed Jewish doctors and nurses.)