The general rule of melee weapon attacks is, that you use STR unless otherwise specified.
The Spell attack modifier of a Ranger is based on Wisdom.
The Primal Companions from TCoE use the Ranger's Spell Attack Modifier but make Melee Weapon Attacks.
My question is, does the use of the Spell Attack Modifier without any further comment suffice to say the attack is made with Wisdom, or does it still use STR by default?
As you noted, the language is (from Beast of the Land):
Maul. Melee Weapon Attack: your spell attack modifier to hit
"Your spell attack modifier" means just that. The specific rule defined in the primal companions' stat blocks beats the general rule determining melee weapon attacks.
For rangers, the spell attack modifier is defined as:
Spell attack modifier = your proficiency bonus + your Wisdom modifier
So, yes, the attack is made with Wisdom, not Strength.
