No, doing the math.
Suppose that at present the vertical launch orientation adds 2 to 5% to the launch costs, and the structural penalties and extra engines required for a horizontal launch would reduce the payload by 30 to 50%. If you made the switch now, the dollars per pound would be 2 to 3 times higher, so we don't do that. But as you start building fully resuable stages with low-cost, high reliability engines, your launch costs drop to a tenth of what they currently are. But the costs of that vertical processing are undiminished, if not increased, because once your stack becomes resuable you have to haul the empties vertically, too. If the vertical costs are undiminshed and you drop the launch costs 10 fold, then that 2 to 5% added expense becomes 20 to 50% of your launch cost. If the expenses increase further due to the empties, the vertical processing could be the majority
of your cost, and will be the determining factor on your flight rate.
So you have two companies, the Vertical Corporation whose rocket delivers twice the payload of the Horizontal Company. But to do that, they have a fourth the flight rate and four times the personnel and support costs of the Horizontal Company. Per man-hour they can only launch an eighth as much as the Horizontal Company, and their investment in support equipment is about eight times higher. They go out of business and the Horizontal Company spawns spin-offs and copycats, and people used to the horizontal launch of rockets five and six hundred feet long, which are as ordinary as a Harrier or F-35 takeoff, wonder who would be insane enough to think you could stand such a thing on its end and make any money at it.
I point this out because the SLS stack is already limited by the door height of the VAB, Congress is never going to approve an even taller building, and no private company is going to try to build a rocket maintenance shed that 700 feet tall. No private company is going to order a 6 million ton crawler or build a giant launch tower because they can't afford it. Even if they did, the structures would be tied up with vertical integration and month per flight processing times while their horizontal competitors could be launching flying machines on a daily basis with a tenth the personnel.
If we had to stand airliners on their ends to get a plane in the air or land one we'd still be riding trains because an airline flight would be a very rare and expensive show. Is it any wonder that spaceflight is rare and expensive when the launch configuration can't be anything but?