Your logic is not wrong, I would like to further explain my train thought: Warning I’m going off on tangent.
When you are a new player and you are still working on leveling up your main team, many ppl will use non stop their 1/2* as feeders (leveled or not) and keep very few 3* if any, and use them for leveling up their main team. They tunnel their efforts into “maxing” their main, understandably wanting to make faster progress in their Pve/Quests.
But, truth be told, keeping leveled 1/2* and all 3* (even non leveled) wont slow you down that much, as far as leveling your big 5 team goes. Now, hoarding this heroes will slow you down a bit, but give you a lot of resources for war.
As for war, the whole idea is to not drop there 5 random non leveled heroes but to drop in 5 color stack FAST heroes (so the more options you have the better), your whole objective is to bust low level team tanks or to hunt down teams that have stacked 2, 3+ a color. You may get lucky and kill it, but chances are you will get stomped in 5/6 turns BUT with a x5 color stack even 3 tiles in 5 turns is A LOT of dmg and if you manage to charge 1 fast ult you get an extra benefit (not a lot of extra dmg but better than going in with average+ ults that most likely very rarely will be used in a 5/6 turn fight).
I’m not saying to keep 1/2* non leveled heroes every time, just to do it the day before a War stars and eat them once you have use them with your flags. As for any 1/2* leveled hero, keep them even if they may be worst than a non leveled 3* they can still come in handy (marginally but still the slowing in progress you do by not eating them is not that big of a deal, imho).