Agree with the above, we built and run a ticketing platform, the actual transaction of purchasing the ticket at the final step in the funnel is not the bottleneck.
The shopping process and queuing process puts considerably more load on our systems than the final purchase transaction, which ultimately is constrained by the size of the venue, which we can control by managing the queue throughput.
Even with a queue system in place, you inevitably end up with the thundering heard problem when ticket sales open, as a large majority of users will refresh their browsers regardless of instructions to the contrary