We have bumped target to chrome:75 as stated in change log. The main reason for that was to improve performance and decrease size of the bundles.
This should create no problems for modern browsers.
I see that you mention sencha cmd and it is not clear to me how do you use UMD bundles with Ext JS. Give us more information/sample please. It may be possible to configure cmd to bypass UMD processing/compiling or it may be necessary to use webpack re-transpile the bundle so that cmd is satisfied.