[obican]

It seems that you are still struggling with dilemma  about this "excellent" lens.
I've tried to help you and asked an question. For you and Brightcolors was self evident that ultimate quality is priority nr 1.
Sigma art series makes fantastic lenses especially for your - insane IQ, price that many amateur can afford..
Yes it is heavy it, it is awakful and fragile, but who cares - remember in the past we have another crazy group of guys. - People with Large format cameras - they ware walking with 25kg equipment, their cameras ware complicated and fragile too. The development cycle in that areas was also moved with slow pace,But they ware prod that they can made pictures with the bast IQ. Even more they think that they ware the best photographers.
The times moves on, lage format died but that group of people still exist.  Here we are Sigma serves them.
For me you question is simple - Do you need ultimate IQ?
If yes - prepare to carry 25kg equipment and doubt anymore.

Large format cameras usually cost a fraction of what you've stated, 4x5 cameras like you've shared can be even lighter than a full sized DSLR + the Sigma lens we're talking about. Moreover, you don't carry them on a strap around your neck. You just load them in a backpack and unpack them on location. Therefore, they are much easier to carry than some DSLR systems.

Please notice I haven't included the weight of the tripod you'd need .