I'm by no means a Developer... One of our staff insists on 'the simplest of apps.' Which means I'm poking code until it breaks, then undoing my last poke.
I had the opposite problem in the Draw Widget. Toggles were off by default, when I wanted them selected.
In the #\widgets\Draw\Widget.html, I made an alteration:
<div data-dojo-attach-point="areaMeasure" class="draw-item jimu-symbol-chooser">
<div class="header applied" data-dojo-attach-point="areaMeasureHeader" data-index="areaMeasure">
<!-- <span class="arrow jimu-float-leading jimu-trailing-margin05" ></span> -->
<span class="item-title">${nls.showAreaMeasurement}</span>
<span class="toggle-draw jimu-trailing-margin1" data-dojo-attach-point="areaToggleDraw"></span>
<span class="toggle-draw jimu-trailing-margin1 jimu-toggle-button checked" data-dojo-attach-point="areaToggleDraw" id="jimu_dijit_ToggleButton_1" widgetid="jimu_dijit_ToggleButton_1" role="button" tabindex="0" aria-pressed="true"></span>
</div>
I'm not really done poking yet, but this change had the desired effect: selecting an area draw tool and using it immediately adds the area label.