Quote from Boreez »Angrath, Giant Growth and Samut's Sprint are completely trash cards in Standard. GG hasn't been a viable constructed card in ages, and sprint might be even worse. What you're talking about is a casual deck, not competitive.
I'm coming at this from a bo1 perspective on Arena. You must be able to beat aggro for bo1, and giant growth can be a fine card to do so. It does help against control too, if you know how to wait for the right moment to play a pump spell. I can beat Teferi control in bo1, it's hard, but it does happen. When it happens it's because I could be aggro enough to kill them before they can set up. When I don't kill them, they are often at 1-3 life before they stabilize and come back up. Giant growth would help in these scenarios.
I'm trying to get at the fact that these cards may be good in a more aggro version of the deck. Yes, you would build your deck to be much lower to the ground in order to enable these cards, and you still wouldn't want more than like 4 max. However, I can see a single giant growth being good in just about any version of the deck. We have access to haste/trample/flying creatures... Just make sure you don't get blown out with a removal spell after casting it. Yes, it takes a bit of maneuvering and planning, that's why you limit the number of copies you play so you only see 1 copy a game at most.
I've raced mono-red multiple times with my deck list, it's just that aggro for bo1. Giant growth helps the deck become even faster possibly... I don't think it should just be discounted out of hand because it didn't make deck lists in the past. You can't directly compare cards to past standard environments they were in because we are in a different environment right now (which is still totally theoretical.) Perhaps a better comparison is how long has it been since a combat trick this good has been printed? This is basically the premium green combat trick to which all others are compared. Combat tricks aren't needed that much, but they can find uses as Collision // Colossus has done for us already with this deck.