While I emphatically agree with this viewpoint, I'd caution that a. this doesn't stop the rest of the EN from destroying ~all of our outlying farmland and causing us to starve (also, killing probably most of the population of Fire, I don't know how much of Fire' population is concentrated in Leaf) and b. the more villages get involved, the higher the risk is of one of their ninja having some esoteric hack that bypasses our defenses. "Destroy any chakra construct if you can touch it for a minute", say. I still agree it's not worth worrying too much about the reaction of the rest of the EN, since even if they have such hacks we can probably still kill them from inside our bubble before they can use them and we can buy food from the Seventh Path clans if it comes to that (or make a "conjure food and water" rune or something, but that might not actually work), but it's not "we win GG EZ".
(Actually, water might be a serious problem in a siege. I don't know how Leaf normally gets its water, but whatever the source it would presumably be cut off by Force Dome and Iron Earth together, and there may or may not exist ninjutsu that create real water in the same way that MEW or MARI creates real granite. It might be worth tossing a prep day at a "create water" rune.)