Agreed that SPI can sometimes be hard to evaluate which leads to it being underrated by some. However, I think when it’s good, it’s obvious it’s good even if you can’t put a number on it like extra commerce due to FIN or expenses saved through ORG. In my current isolation game switching between vassalage (cannons) and nationhood (rifles) was the only way to get CR2 cannons because I don’t have a religion. Pretty sure my breakout war would have failed without it and that’s ignoring the more minor benefits like actually being able to use free market for a few turns before going communism, which is never worth it without spiritual but here meant perhaps 15 turns of an extra 12 overseas trade routes.
The other great thing about SPI is that if you’re comfortable going culture, SPI plus marble gives you a very high win percentage on even difficult maps - cheap temples, easier to avoid DOWs and easier to get cultural rivals to switch out of free speech before going back into it yourself. This isolation map is the worst land I’ve won on deity with - just because you’ve got beaverless ice next to your BFC doesn’t mean you can’t have desert too, one happy and no grains on the island. i don't think i could have won it militarily. i think if more people went culture from time to time, SPI would get more love.
The trouble is that it really offers nothing for an early rush and on maps where killing an agressive neighbour sharpish is the only path to victory. FIN and PHI can at least give you a little boost here even if it's not where they really shine. It can be helpful for the recovery phase on maps like that but only if you can get there. Based on that, I'd place SPI in the tier below PHI and FIN.
Re AGG, I don't quite agree that it only helps with axe rushes, although that's its main strength. I think both AGG and PRO help a fair bit with games where drafted rifles are key, which happens a lot in isolation. Being able to go pinch with one promotion can be very useful, not so much when attacking because cannons will do most of the work but for preventing your stack from being attacked open field: If you can get your units to be slightly stronger than the AIs, there seem to me to be a number of AI that won't dare attack your stack because the odds for the first attack are too poor. Given how overpowered first strike is, I do think this makes a difference. I don't think it makes a difference often enough to really save the trait but I do think it retains some use up to rifling.
