There are various ways to gain thematic companions in D&D. Here are some of them:

• roleplay
• spells like animal friendship, animate dead, find familiar, and find steed
• the Beast Master

Each way gives a different experience. Choose the one that best fits your story! #DnD

— Jeremy Crawford (@JeremyECrawford) August 9, 2018

Sure, but a class feature that guarantees a thematic companion, should give a thematic companion.

If you had an aquatic ranger archetype, but made having a companion with a swim speed impossible, it’d feel wrong. Same deal for Pact of the Chain and certain warlock patrons. I understand that you'd like Pact of the Chain to match up with each patron. That's not how we designed it. The feature is patron agnostic. But message received!

— Jeremy Crawford (@JeremyECrawford) August 9, 2018