See https://github.com/dlang/dmd/pull/9014#issuecomment-667704187 for an extensive overview. TL:DR. isDynamicArray should use an is-Expression instead of additional templates.
@MoonlightSentinel created dlang/phobos pull request #7574 "Fix Issue 21103 - isDynamicArray instantiates unecessary templates" fixing this issue: - Fix Issue 21103 - isDynamicArray instantiates unecessary templates https://github.com/dlang/phobos/pull/7574
dlang/phobos pull request #7574 "Fix Issue 21103 - isDynamicArray instantiates unecessary templates" was merged into master: - 7bea4c78b90c4ca182298ebc758a41edc7227315 by MoonlightSentinel: Fix Issue 21103 - isDynamicArray instantiates unecessary templates Use an `is(...)` expression to do the actual check but include a workaround to reatin the old (buggy) behaviour regarding enums (for now). https://github.com/dlang/phobos/pull/7574