Generally the best approach there is to elevate a bunch of your smartest engineers into an architecture team that a) set good standards but also b) appreciates

Generally the best approach there is to elevate a bunch of your smartest engineers into an architecture team that a) set good standards but also b) appreciates the nuance of problems sufficiently to know when to deviate. A small team can probably only handle one tech stack, an org with 10 teams can probably handle 10 stacks if they needed to but can get efficiency by standardising on some number less than 10. However making those calls shouldn't be coming down from the CTO, it should be made among the architects that actually design and build the systems.