"Big" isn't sustainable in space flight for any amount of time, unless you have an infinite supply of either capital or political will. More spam, still no point.
An opinion that you don't share isn't 'spam--its an opinion.
Big is sustainable, as we saw with 100= shuttle flights with not all that interest--because the STS was a LEO only system--but it was a defacto HLV in terms of mass to orbit--that that proves me correct.
In terms of future tech--al we need do is look to the past--and support such systems as opposed to sniping at them from the interwebs
The Shuttle was barely sustainable, and only by sucking up most of NASA's budget. It should've been retired by the late 1980's, but they couldn't afford to replace a system that was working, and due to the very low flight rates none of the Shuttles were near the end of their operational lives, which was supposed to be pretty short.
One problem with SLS is that it's the same as a host of mid-1970's Shuttle-derived cargo designs. It's not reusable and the architecture doesn't offer any way to make it reusable, so the same people who built external tanks for the Shuttle will be building modified external tanks that will be thrown away, along with the either RS-25E or RS-68 engines, which are very expensive.
It's an example of NASA not innovating, nor driving the technology in new directions, like coming up with cheap
expendable liquid engines, or liquid strap-ons with propellant cross-feed, or reusable first stages that land vertically, or any of the other approaches private firms are pursuing. The projected flight rate of the SLS is going to be less than the Shuttle, depending on whether they design a payload for it.