I'll never understand where people get their ideas on Yu Yevon from.

For one thing, he clearly wasn't a tyrant as every single one of the remaining people in Zanarkand willingly became Fayth for the summoning of Dream Zanarkand.

Sin only exists because from within Sin, he could perpetually keep Zanaraknd alive "if only in a memory" in the form of Dream Zanarkand. it had nothing to do with ruling forever or creating a Spiral of Death.

Finally, it was Yunalesca, not Yu Yevon or the leaders of Bevelle, who did what you said.

"On the eve of Zanarkand's destruction, Lady Yunalesca... had fled to safety with her husband, Zaon. Later, the two used the Final Summoning to defeat Sin. Yet the people of Bevelle still feared Yu Yevon.
It was to quell his wrath that they revered him, and first spread his teachings.
And so were born the temples of Yevon.
I suppose it's possible Yunalesca had planned it that way from the start!
A fair trade, she defeats Sin in exchange for her lord father's honor."