The point here is a different one I think. It's not that everyone and their dog will create their own version of things, this will probably not happen at such a huge scale for the reasons you mentioned.
What might change is that the barrier to enter the market is lowered so someone without gigantic investment and years of time could actually come out with e.g. a JIRA competitor ticking all the boxes. This drives the vendors margins down. Also might give the buyer more negotiation power if you can say "then we just do our own version".
There is a lot of vendor lock in the software world just because it's just too hard/risky to do a full featured competitor, that might change and eat into the margins of especially those vendors. For those who also have healthy competition, the relative dynamics probably don't change much, agreed.
What might change is that the barrier to enter the market is lowered so someone without gigantic investment and years of time could actually come out with e.g. a JIRA competitor ticking all the boxes. This drives the vendors margins down. Also might give the buyer more negotiation power if you can say "then we just do our own version".
There is a lot of vendor lock in the software world just because it's just too hard/risky to do a full featured competitor, that might change and eat into the margins of especially those vendors. For those who also have healthy competition, the relative dynamics probably don't change much, agreed.