Not true in general or the more important specific case of a discharged battery getting 'hammered' into cutoff over and over.
In the general case, the battery charges part of the time (heating) and discharges part of the time (when the heater comes on, heating even more). Total heat buildup is higher than charging and using at separate times. Heat is a serious enemy of battery life, extra heat is to be avoided.
In the unfortunate case of a discharged (or nearly so) battery, the discharges when the heater comes on can force it back into shutdown/protect several times a minute. This was found to be destroying batteries in ESV, literally killing them in a few such events, so the latest software no longer allows this. Yes, the maker took this popular feature out......
We asked for (some might say 'demanded') this feature. 'Use while charging' makes sense in things like Cell Phones where the discharge is longer than the charge, but in cases like our here IMO this is not a useful feature and should be avoided. The fact that it takes longer to charge tan discharge is a clue.
OF