I'm more exaggerating for effect than arguing from ignorance.
Though I should point out that companions don't lose abilities like pounce or trample so you can still get multiple attacks per round with a companion, just not quite as reliably as you could with multiattack. Also, companions add your proficiency bonus to damage rolls in addition to their ability score modifier.
At 3rd level that makes a wolf or bear companion's damage roughly equal to a ranger with a crossbow, assuming the ranger has an 18 dex. A panther companion will do roughly 1.5x this on a pounce.
The Ranger can burn spells to increase their damage, at best getting extra d6 for three encounters out of the day, which is about half of what the DMG recommends they face. And on average, the panther still does slightly more damage on a pounce.
This gets worse as you level up, because the companion gets the same ability score increases as the ranger, has farther to go before it caps out at 20, and the proficiency bonus keeps going up as well. Granted, the ranger also gets some better spells to crank up their damage output, but those are still only usable a limited number of times.
By the time you hit level 20, the ranger gets one attack for 1d10+5 to their companion's two attacks doing 2d4+11 each. If it's a panther or there are multiple enemies within 5ft, the companion can get even more attacks--up to the number of adjacent enemies +1 If the ranger has feats, (and that is "if", since feats are an optional rule in 5e) they can get up to two attacks at 1d6+15, which is only five points more than the companion does on average. Using spells, it looks like Beast Conclave Rangers cap out at an average of 70 points (2d6+30+6d10) in a single round using Crossbow Expert, Sharpshooter, and Hail of Thorns cast with a 5th level slot. That's a little over twice what their companion can deal on average to a single target, but the ranger can only do that twice a day.
It is worth noting that while the companion can get in a lot more attacks if it's surrounded, each of those additional attacks have to target a different creature. Since Hail of Thorns deals damage over the same radius (5ft), the ranger has a higher theoretical damage output under ideal conditions. But still only twice a day compared to the companion's at-will impersonation of a furry blender.