How strong are the 4 Stars with Dupes compared to the 5 stars without? And is the Welfare Madoka we get a True 5 star or like a weaker version of a 5 star in between 4 and 5 or at 4 star power level?

So Basically Title.

I think its fair to assume on a Base 0 Duplicate level a 5 star is generally (ofc it will vary from case to case) stronger than a 4 star as is normally the case in games with rarity. However with Dupes giving stats and added effects how many Dupes does a 4 star need to equal a 5 star with 0 dupes and at max Dupes (lets say 5) what lvl of dupes are they equal to a 5 star ?

Also Madoka the free 5 star we get can be gotten at max dupes. Is she at the lvl of a 5 star (as in her maxed duped state has similiar stats and output to a max duped 5 star like say Iroha or the 5 other Madoka) or is she more in line with a 4 star in power?