I tried performing joins from studio with this change enabled/disabled
With the change enabled there is an increase in the ping spike. However, the current state on production clients & studio for the general public is with the change disabled, and there are still hundreds/thousands of ms ping even with the change disabled, so the core of the problem is not the change I linked.
The change that I linked is intended to reduce the overall impact on ping when joins happen. If you catch a server microprofile, you will see that the ping is caused by an elongated frame, which in turn is triggered by processing many instances on join. The change I posted earlier is part of a larger initiative aimed at reducing that time, so this general problem is on our radar. Reducing this time on join for games with many instances is multi-faceted, it is going to take a significant amount of engineering effort (time) to reduce.