Ehh this is obviously a controversial opinion on this thread, but it's pretty common to have exclusive rewards locked behind features like this.
The day they released the brac scroll/other rewards as Kickstarter-exclusive items meant that there will always be a limit to what people can access. I will never get a G1 Bracc. I will never get all the KS companions. Some people may never unlock all the referral companions.
Sure, the bracc scrolls, G1 Braccs, KS companions etc. are technically obtainable as they are not soulbound (but priced beyond what I could ever save), but the referral companions are also obtainable without necessarily needing to recruit new players. The retroactive referral that's been introduced (assuming it sticks around) still allows people who are unable (for whatever reason) to get the companions if it is important to them. I think being able to buy referrals defeats the purpose of a referral system, but it's been allowed, so it's an option.
If the argument is the referral companions should be accessible by other means, then I would say remove the companions all together and make it something generic a moonstone/pebble reward, or just make the companions basic like any other easily available companion and not be a special reward at all. But that would require for LW to never offer special rewards for any limited-time promotion, as it's the same core issue and these concerns will keep reoccurring (and I guess technically that should include re-releasing KS rewards/companions). Either you have exclusive rewards for exclusive activities, or you don't.