This is true. I usually don't hit them with that grenade until after I've shot them at least once so they will burn to death. I also find it hilarious to chuck a solar grenade at my own feet and have a melee battle with flame shield on. I hit them once, they burn and my grenade incinerates the rest of their health while I'm still sitting there full health with just my shield gone. Sunsingers are the damn melee kings if you use their perks right. A striker is a champ once maybe twice per life but the recharge is so fast on sunsingers you can do it in every single encounter.