Yeah, I can see that as being too powerful. Not something I'm likely to hand out without some thought.
But, I wonder how much impact how groups roll initiative change things. For example, if you do group initiative for monsters - where basically all the monsters go at the same time, this would be a huge advantage. OTOH, if you do individual initiative, like I do, for monsters, even with the party getting advantage on initiative, the fact that I'm generally rolling initiative up to seven or eight times in most encounters, means that it's still pretty likely that some of the monsters are going to either go first, or at least second.
This is what I'm talking about when people start reporting their experiences. Small changes in how things are run can have very large effects. Do you use a battlemap or TotM? Is your campaign largely dungeon crawls or something else? Do you randomly generate monster HP? (An option on Fantasy Grounds for example that means that I literally have no idea how many HP monsters have before the encounter starts). How much time is allowed in the campaign? For example, my Lost Mines of Phandelver: Shattered Obelisk game took nearly two in game years to resolve LMoP and about two months to resolve Shattered Obelisk. There absolutely was no downtime in Shattered Obelisk to the point where even scribing new spells into spellbooks was a challenge.
So on and so forth. There are so many variables that making any sort of conclusions is very difficult.
