Well he said he tested that when he was at GGG's office, so they probably had a prebuilt setup for him to use rather than a full minmaxing setup. He does mention GMP in the description, but there's a fair amount of good supports for the build and the aoe seems relatively decent even without GMP due to having a bunch of golems. Shotgunning could be possible sometimes but not sure how often it'd be relevant withotu frostwall, I guess it kinda shotguns bosses with mobs around them with the overlapping explosions but otherwise you need to push the boss into a wall. He has spell echo in there as he mentionned which is to summon 2golems at once for them to benefit from the jewel increased damage on summon, but you could easily cut that for something else to scale better.
Getting the jewels will probably be a pain in the ass now that he made that video however. But I assume the build will clear fine even without jewels until higher tiers, so you should be able to ease into the build.
If I play this league I'll probably play that anyway, seems pretty fun and I like me some summoner builds, over half of my chars now have been variations of summoners. I was kinda leaning towards chaos poison animate weapon this time around since nothing new seemed terrible too interesting but fire golems sounds cool.
Also think the 30% golem effect jewel might see some interesting abuse if stacked with certain non damage golems. Like making someone super tanky with chaos/stone golems in an elementalist build or some shit like that. Not sure how viable it'd end up, but it's interesting that they didn't put a limit on those jewels(like say 3).