Competition and ease of replicability matters a lot in the long run.
"Weak Competition" or legacy players are largely irrelevant, which is an important distinction to make.
I have no doubt in 10 years there will be numerous ways to sign documents electronically and margins will be thin.
Think about cloud storage and other areas with a high amount of competition. All of these things will trend towards margin compression in the long run, almost by definition of being in a competitive/free market.
Cost of switching matters a lot too. It's easy to move from DocuSign to some competitor. It's
more difficult to move from managed MongoDB to managed Postgres, due to having to define some translation layer.
The thing is that we're just early in the digitization cycle so all these first movers becomes pseudo monopolies. That won't last for more than a decade or two.
Highly likely that stock performance for a lot of these 20-100x sales stocks will be very poor over the next 10 years. But you may get a good stretch of high returns in the short/medium term.
Think about when Ford created the assembly line. Did that give them a forever Monopoly on cheap production of cars? There's this attitude that competition doesn't matter in technology, but we can clearly see in things like laptops, routers, hardware etc, that margins became very low after market got saturated.
It's only just the last few years that things like DocuSign were even possible to create.
This is especially true for software where once it's built, marginal cost to deliver value is extremely low. Theoretically, a well designed and cloud native/managed version of DocuSign could be run by just a handful of people in the long run. Do people really expect that nobody will accomplish this in the next 10-20 years?
Where there's margin, there's opportunity.