This isn't an MMORPG with 20,000 people wandering around screaming "LFG."
A fighter needs to be effective enough to be fun for the player who wants to play it, not competative enough to earn a slot in a premier raid group.
It is close enough. If the Fighter doesn't have a vast repertoire of out-of-combat utility, nor of in combat spell, his weapon based offense has to absolutely shine.
Think of it this way: compare 2XCleric vs Cleric+Fighter. We want Cleric+Fighter to be the better choice (maybe not by much, but still better), and accept that 2XFighter just won't work.
Then if Fighter melee=1.5XCleric melee (currently more like 1.1X), Fighter+Cleric has 25% more melee at the cost of 50% of the Cleric utility and healing. Just not worth it, even at low levels where the Cleric utility isn't that extreme.
If Fighter melee=2XCleric, that pushes it to 50% more melee at the cost of 50% of the utility and healing. That might be worth it, at low levels. At higher levels, it won't be.
This is important. It is easy to miss low on Fighters. Really really easy. Very few people complained about Fighters being overpowered in 1e, even pre-UA, and there they started at about 300% of melee-cleric melee and rapidly scaled up from there. The playtest stats suggest that WotC isn't even in the right ballpark, balance-wise.