I'm curious, looking at your frame I'd presume it'd be a sub 8kg bike maybe sub 7.5kg. Even with power meter pedals, I would think going with ERX would offset a bit of the weight. The 105 R7000 isn't that heavy either. Is it your 60mm deep dish Elite Wheels and/or cassette that's adding weight?
I think even the real pinarello is a pretty weighty bike. I definitely didn't go the weight weenie route, the 60mm Elitewheels SLT were about 1750g, cassette is a Shimano Ultegra 11-32. I'm using a cheap set of IIIpro disc brakes, not sure if they're lighter than normal disc brakes. Also, ERX groupset is quite heavy compared to a mechanical groupset too.
Quick question about the saddle bolts, how do you tighten a saddle without a cutout in the middle? I realized that one of the bolt faces upwards, and if there's no cut out in the saddle, I have no idea how to tighten it.