That makes it worse in many senses than a delayed copper
Given that Guardian is an on-play delayed Copper with a cherry on top when you gain it, this statement is false.
Sorry, but no. A delayed copper is Caravan Guard. It literally gives you a copper next turn at no cost to this turn.
Haven dumps a copper back to next turn as well, and like Guardian it reduces your current hand by one. Save can do likewise; nobody ever calls those delayed copper because they do not play like delayed copper.
We have plenty of actual "delayed copper" and Guardian is not it. Guardian anti-smooths your early buying power, taking from the play turn and moving to your duration turn.
LFN:
You have a Haggler in play with a copper - in general would would you: buy the silver/gain Guardian, buy silver/gain copper, buy nothing on no attack boards?
You open $5/2, no attacks, do you buy: the Guardian or nothing?
You are playing a Bandit camp/Alms/Moneylender/+buy game after how many silvers would you buy Guardian (0, 1, 2,
?
In general I will take silver/Guardian over silver/copper pretty much all the time and most of the time I will take that over nothing if I will take silver alone. Somewhere around 1/3 to 1/2 the time I will open Guardian on a 5/2, higher with weaker $5s.
The last is the hardest one, but generally I would say Guardian can be a reasonable move from 2/3 silvers in deck to 1/2 on maybe a quarter of boards.
By far and away, the most common reason to get a Guardian is spiking something next turn. Making a $3/4 into a curse/$5 would be worth a huge amount of the time so I routinely buy Guardian there.
Once I have Guardian in my deck, how do I play it? Not like it is delayed copper like Caravan guard nor like Haven/copper; instead I play like it anti-smooths my deck; this means that deck smoothing may be approached differently - Save an estate if Guardian is in the last hand of the shuffle to have much better odds of spiking a $6 or $7, alternate it with a Haven moving copper to smooth out when I am getting close to regular $5s. When you play Guardian it removes buying power from that turn and raw adds it to the next turn without penalty ... that just plays different than things which delay a copper.