It was discussed many times that religion needs to be changed in civ 7, because it is neither thematic nor is it a lot of fun. Here is a not-very-well-thought-out-yet-but-momentarily-to-me-interisting-sounding (TM) suggestion:
1.) bring back religious pressure. I would even say that religious pressure should be the standard way of converting nearby settlements.
2.) make conversion with missionaries an actual effort and relate it to culture and/or gold. Missionaries should be expensive units (similar to commanders, for example) that you don't build/buy a lot of. They should lose their charges for conversion. Instead, they gain the ability to exert religious pressure on a settlement (regardless of district) when standing on a respective tile. The pressure is not just any value, but you as the player can decide how much culture and gold you want to invest in the conversion.
An example: Rome is Catholic and receives +20 religious pressure per turn towards Catholicism and +3 religious pressure towards Islam (your religion) per turn. Hence, in order to convert it, you need to increase the religious pressure of Islam by +18 per turn, then it would slowly convert as long as you keep your missionary and the task active. Through the years, Rome has accumulated a lot of religion: Catholicism sits at 260 strength, and Islam only at 24. Hence, increasing the religious pressure of Islam by +18 would mean that you need hundreds of turns to actually convert it. So, better to invest 40 culture per turn and 40 gold per turn to create 160 religious pressure per turn on Rome. With that, it will be converted in just two turns, and starts to pressure nearby cities with Islam. Of course, if you remove the missionary right away, Rome will convert back after some time. So maybe keep it some more turns or have multiple missionaries active in the region, so that the pressure of Catholicism overall drops. This system, while complicated, gives the players much more options, more decisions, granularity, and a defense (as you can use missionaries on your own cities as well). It also ties religion closer to the culture and your overall economy output of your civ.
3.) It's possible to include great works or wonders in the system: if a settlement hosts a relic of your culture or religious wonder, it boosts the religious pressure of your religion that this city exerts. That way, permanently converting foreign settlements of a civ that is also religious is more difficult, and requires to do it more as a planned campaign, while rather non-religious civs can be converted with more ease.
1.) bring back religious pressure. I would even say that religious pressure should be the standard way of converting nearby settlements.
2.) make conversion with missionaries an actual effort and relate it to culture and/or gold. Missionaries should be expensive units (similar to commanders, for example) that you don't build/buy a lot of. They should lose their charges for conversion. Instead, they gain the ability to exert religious pressure on a settlement (regardless of district) when standing on a respective tile. The pressure is not just any value, but you as the player can decide how much culture and gold you want to invest in the conversion.
An example: Rome is Catholic and receives +20 religious pressure per turn towards Catholicism and +3 religious pressure towards Islam (your religion) per turn. Hence, in order to convert it, you need to increase the religious pressure of Islam by +18 per turn, then it would slowly convert as long as you keep your missionary and the task active. Through the years, Rome has accumulated a lot of religion: Catholicism sits at 260 strength, and Islam only at 24. Hence, increasing the religious pressure of Islam by +18 would mean that you need hundreds of turns to actually convert it. So, better to invest 40 culture per turn and 40 gold per turn to create 160 religious pressure per turn on Rome. With that, it will be converted in just two turns, and starts to pressure nearby cities with Islam. Of course, if you remove the missionary right away, Rome will convert back after some time. So maybe keep it some more turns or have multiple missionaries active in the region, so that the pressure of Catholicism overall drops. This system, while complicated, gives the players much more options, more decisions, granularity, and a defense (as you can use missionaries on your own cities as well). It also ties religion closer to the culture and your overall economy output of your civ.
3.) It's possible to include great works or wonders in the system: if a settlement hosts a relic of your culture or religious wonder, it boosts the religious pressure of your religion that this city exerts. That way, permanently converting foreign settlements of a civ that is also religious is more difficult, and requires to do it more as a planned campaign, while rather non-religious civs can be converted with more ease.