I think you are absolutely right on this point. Actually, I think the whole US MR market is lagging behind. I do not know whether is because Soylent’s shadow, or the fact that you live in a single country (whereas in EU many countries have their MR brands) or other factors (probably a mix of many).
As a curiosity, there is one area that US has more of; keto meal replacements. It is a fairly competed niche. And in this niche is one of the other RTDs; Sated Drink (currently in preorders).
Saturo is pretty similar to Soylent; similar nutrition wise and taste wise (although some prefer Saturo, and I guess others Soylent). For me, they are both meh. It is interesting that Saturo is making the jump to the US, since they are the RTD with most similarities to Soylent. They just have more flavours, and different size bottles.
More about saturo here: https://latestfuels.com/saturo/
As for other RTDs, my favourite must be YFood, a German brand that makes milk based RTDs. I find their taste to be more pleasing, as well as, 33g of protein for 500kcal is nice.
Mana Drink is meh. Pretty similar to Soylent original.
Feed. has very interesting RTDs, especially if you consider pre-powdered bottles as RTD. They have a really weird range of flavours like Spicy Tomato or Carrot&pumpkin, as well as more normal ones. They are fairly pricey unless bought in bulk.
And many that I haven’t tried, Trinkkost, PlennyDrink, Your Pop Up Meal…
I hope that Plenny Drink comes to the US soon.
As for the US RTDs…
There is Ample that offers premium organic meal replacements (they offer pre-bottled powder).
And the Canadian Vital house (same format as Ample) that offers high protein MRs.
What I really hope is that Huels finishes developing their RTD soon. That is going to be a market changer I feel.