Let me counter that specific example with a much more general breakdown. Disclaimer: I haven't taken a math class for twelve years, and might be talking out of my ass.
With Itinerant Preachers, each religious city reaches 69% more tiles than it would otherwise. With Religious Texts, each religious city (eventually) applies 50% more religious pressure than it would otherwise. At roughly the same time Religious Texts really gets going (Banking), you'll get your fifth trade route (maybe six, maybe seven if you somehow snagged both the Colossus and Petra). So that's bonus religious pressure to five/six/seven other cities, if you're willing to forego the potential advantages of domestic trades routes, of sending multiple routes to a single city, of sending routes to cities within ten tiles, etc. You could actually make the same decision with Itinerant Preachers; you'd just have to pick your destinations even more carefully (and probably pass on more potential gold in the process) and make longer, riskier routes.
The difference, then, all other things being equal (which, obviously, they wouldn't be in practice, but let's just let that go—IP will actually be better in practice because it starts so much stronger), is that RT gets 15-21 more pressure (3 per city) from trade routes. Let's say it's 18; six trade routes. IP generates 19% more pressure than RT, assuming an infinite, even distribution of cities. If a RT religion were generating 100 total pressure without the trade routes (mathematically impossible, yeah, just bear with me, it's hypothetical), it would now be generating 154 with them. An IP religion would be generating 155. That's our breaking point—100 pressure, give or take some depending on how many trade routes you're willing and able to commit to spreading the faith. If you have four religious cities within ten tiles of one another, that's 81 total pressure right there (with RT). In other words, 100 total pressure is nothing. Assuming even a roughly even distribution of cities across the map, IP is way, way better, and that's even before you consider the advantage it has pre-Printing Press.
There are definitely map setups where Religious Texts could be better. On a Small Continents map with high sea level, you might have cities clustered together so that every city on a continent is within 10 or so tiles of every other city, and each continent is at least 14 tiles away from the next. Religious Texts would obviously dominate there. On almost any Pangaea, Continents, Fractal, or even Archipelago map, however, I think Itinerant Preachers crushes Religious Texts. Assuming my rusty math holds up.
With Itinerant Preachers, each religious city reaches 69% more tiles than it would otherwise. With Religious Texts, each religious city (eventually) applies 50% more religious pressure than it would otherwise. At roughly the same time Religious Texts really gets going (Banking), you'll get your fifth trade route (maybe six, maybe seven if you somehow snagged both the Colossus and Petra). So that's bonus religious pressure to five/six/seven other cities, if you're willing to forego the potential advantages of domestic trades routes, of sending multiple routes to a single city, of sending routes to cities within ten tiles, etc. You could actually make the same decision with Itinerant Preachers; you'd just have to pick your destinations even more carefully (and probably pass on more potential gold in the process) and make longer, riskier routes.
The difference, then, all other things being equal (which, obviously, they wouldn't be in practice, but let's just let that go—IP will actually be better in practice because it starts so much stronger), is that RT gets 15-21 more pressure (3 per city) from trade routes. Let's say it's 18; six trade routes. IP generates 19% more pressure than RT, assuming an infinite, even distribution of cities. If a RT religion were generating 100 total pressure without the trade routes (mathematically impossible, yeah, just bear with me, it's hypothetical), it would now be generating 154 with them. An IP religion would be generating 155. That's our breaking point—100 pressure, give or take some depending on how many trade routes you're willing and able to commit to spreading the faith. If you have four religious cities within ten tiles of one another, that's 81 total pressure right there (with RT). In other words, 100 total pressure is nothing. Assuming even a roughly even distribution of cities across the map, IP is way, way better, and that's even before you consider the advantage it has pre-Printing Press.
There are definitely map setups where Religious Texts could be better. On a Small Continents map with high sea level, you might have cities clustered together so that every city on a continent is within 10 or so tiles of every other city, and each continent is at least 14 tiles away from the next. Religious Texts would obviously dominate there. On almost any Pangaea, Continents, Fractal, or even Archipelago map, however, I think Itinerant Preachers crushes Religious Texts. Assuming my rusty math holds up.