Do you have source information for this? Because the development information for this card found here says:Quote from xaltair »...
I can pre-evaluate cards before they become famous and played in popular decks.
path of mettle is such a card, it is a mid-game card that is meant to be flipped on turns 6-9 and help to end the game or do the last few points of damage to the opp much like ramunap ruins was used. It's not meant to be flipped over on turns 3-5 unless you need to use the extra mana ability.
Which brings me to the quoted text above, if you have a deck where most of your creatures are 1 drops or 2 drops it means that by the time you will get to cast path and flip it you will already have won the game, or you will not have any creatures on the board because you opp will have killed them. A 1/1 or 2/2 will simply not survive more than one turn, so if you draw path of turn 5-6 and want to cast it and flip you won't be able to because you won't have any creatures on the board to attack with, or maybe you'll have one only.
Path was not meant to be played in an aggro deck, but in a "big red" or mid-range deck that can flip it any turn past turn 5, so having creatures that come down on turn 4 or 5 and can survive past turn 5-6 means that path will get flipped on those turns. That is the reason why this card works in a deck with Hazoret at 4 mana and Glorybringer at 5 mana and both of those cards can flip it.
This card was, in my opinion, the weirdest card in the set. It made sense from a flavor standpoint. The playtest name of this card was "Hallway of Traps," and you had to be quick and vigilant to get through the hallway. When you got to the top of the tower, you could shoot things down with the activated abilities. Despite the story the card was telling, the card looked super weird to me. I built a lot of decks with this card and actually found it to be versatile. I had to choose carefully what creatures I would put in my decks, and sometimes the triggered ability on the front half wouldn't do anything, but after it flipped (which was surprisingly easy), I had a mode that was strong against aggro decks and a mode that was strong against control decks. The real world has had success in building decks with this card, which is always a good feeling for the person who did the most playtesting and iteration on it.
Further, the information for Relentless Raptor says:
Not all Dinosaurs are big and expensive. This card was aimed at an aggressive deck with a low curve, but with its 3/3 body it still had a Dinosaur feel to it. It plays particularly well with Path of Mettle.
My reading of this doesn't seem to support your contention that it is not meant to be used in aggro decks. Without source documentation, stating your interpretation so definitively also doesn't seem helpful.