It can be, but a senior who is well-versed in the fundamentals and has some exposure to complimentary tools in other ecosystems is not going to have a problem c

It can be, but a senior who is well-versed in the fundamentals and has some exposure to complimentary tools in other ecosystems is not going to have a problem coming up to speed with those tools. What they're going to spend more time on is: learning how you decided to solve your problems with your knowledge of those tools and how you decided to fit it all together.