Multattack doesn't work the way you want as per the word of the sage, Jeremy Crawford.
Well the new official Errata trumps Jeremy Crawford... so what he said in the past is obsolete due to what he approved as official.
Bestial Fury (p. 93). This section has been changed to “Starting at 11th level, when you command your beast companion
to take the Attack action, the beast can make two attacks, or it can take the Multiattack action if it has that action.”
But also its crazy to me that challenge rating of 1/4 is the limit for Rangers when Mechanical Servant for Artificers is "Select a Large beast with a challenge rating of 2 or less" which you use for the stats so they get
Polar Bear MM p334 as an option that.
AC12 HP42(5d10+15) Speed 40ft swim 30ft Perception +3 (13 passive)
60ft dark vision - only feature from Cave bear variant
Keen smell (advantage on perception checks with smell)
Multiattack. The bear makes two attacks: one with its bite and one with its claws.
Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 9 (ld8 + 5) piercing damage.
Claws. Melee Weapon Attack: +7 to hit, reach 5 ft ., one target. Hit: 12 (2d6 + 5) slashing damage.
Mechanical Servant adds:
• It can’t be charmed.
• It is immune to poison damage and the poisoned condition.
• It gains darkvision with a range of 60 feet if it doesn’t have it already.
• If you are the target of a melee attack and the servant is within 5 feet of the attacker, you can use your reaction to command the servant to respond, using its reaction to make a melee attack against the attacker.
While I get the Artificer is not finalized since the ranger only gets:
• Add your proficiency bonus to the beast’s AC, attack rolls, and damage rolls, as well as to any saving throws and skills it is proficient in. Its hit point maximum equals its normal maximum or four times your ranger level, whichever is higher.
• You can use your action to verbally command it to take the Attack, Dash, Disengage, or Help action.
It seems to me the Artificer companion allowing higher CR choices with attacks on reactions make it a better supplement than the Beast masters since your losing the Rangers action to attack on its own where the Artificer can play normally but use their companion to defend themselves. Seriously an Artificer fights a Beast Master ranger its going to rock its world and this is random add on feature for the Artificer while its the design for the Beast Master. If they had added just the reaction bit to the Beast master and opened up the CR for the beat master at level 6 and allowed for an upgrade that would be cool. I know parting with the CR1/4 might be a sad story moment but at the same time when that creature dies at higher level you make the change to something that can keep up, since that's likely to happen anyway.