Your yellow roster
Thank you for the compliment.
Your yellow hero situation is different from your purple hero situation ( edit: actually, I may be confusing you with another user ). This is why I always say “What else is in your roster”
One of the weird things about Empires is 4* 3.60 > 5* 2.60 > 3* 3.50. So Domitia 5* 2.60 will actually be more powerful than Tyrum 3* 3.50 and Balthazar 3* 3.50.
3* ascension items are 3x as plentiful as 4* ascension items so by the time you get the 6x Tabards and 8x Trap Tools for a 5* purple, you have 18x Trap Tools or 10x extra trap tools. You can use that to level two 4* heroes to 4* 4.70 or two 5* heroes to 4* 3.70 . If you had better options for 4* purple ( I am drowning in them so I have the problem of too many for my purple Hero XP ) but without better options, Domitia at 5* 3.70 might be your best bet.
Gem summons
Guardian Jackal gets all the attention ( for a lot of good reasons ) but Guardian Falcon is actually the more powerful hero at both 4* 3.60 and 4* 4.70 because his Elemental defense debuff affects up to 3 targets and his defense stat is comparable to a red 5* hero BEFORE you use emblems on him. With the addition of Wilbur to the game, Guardian Falcon is over powered.
I will keep doing three 1x summons per Guardians until I get Falcon. I would not mind a second Jackal or a second Falcon once I get a first one.
In fact I just power leveled the following rainbow team from 4* 4.50 to 4* 4.70 so I could put emblems on them for war- Tiburtus 4*+5, Jackal 4*+1 ( has to compete with Scarlett 4*+7 ), Kiril 4*+1 ( has to compete with Proteus 4*+7 ), Boldtusk 4*+5, Hansel 4*+1 ( has to compete with Rigard 4*+8 ).
Until I got Jackal and Joon, I used a 4* 4.70 and a 4* 3.60 Wu Kong in war. Not a lot of purple centers at my alliance level, or my Wu Kong 4* 3.60 would still be getting a lot of use.