FrogReaver
The most respectful and polite poster ever
It doesn't have to be as strong as the fighter. It just has to stand in melee long enough to take most of the attacks the fighter would have.There is an opportunity cost.
The Wizard who spends the higher slot to Summon, to keep one or two foes busy, now can do nothing else with that slot. Those summonees wont last long, the Wizard deals even less damage, and the Wizard is in imminent danger. This is how all-Wizard parties TPK. Even if the Wizard survives this one encounter, there is likely an other one soon after, when there are even fewer slots available.
We are no longer playing 3e. The 5e spells fail to "replace" a Fighter.
A level 5 GWF has 17 AC (maybe 18) and 44 hp (@ 14 con).
A Summon Fey using 1 level 3 slot has 15 AC and 30 hp.
Seems close enough to fulfill that purpose for me.