2. Shane Waldron does not have a history with mobile quarterbacks
If you look at the quarterbacks that Shane Waldron has worked with throughout his entire career, they have been pocket-style quarterbacks. He started his career working with the New England Patriots and Tom Brady, after all. He went to Notre Dame to coach Brady Quinn with Charlie Wess, and during his other stints in college, he worked almost solely with pocket passers.
When he jumped back to the NFL, he spent a year with Washington with Kirk Cousins before heading to Los Angeles to work with Jared Goff. Lastly, while he did work with Russell Wilson for one year, it was not the best marriage, and Waldron got a lot more from Geno Smith, someone who is much more comfortable playing from inside the pocket.
Sean McVay's offense has always worked with players who are best in the pocket, and Waldron has specifically worked with this style of quarterback.
Again, you have to ask if Waldron really wanted to take this job to try a bunch of new things he has never done before or if he wants to install a scheme around a rookie quarterback that he thinks can fit into his offense.