But that does not apply when you have a biont as foreign gene in a macroorganism: in that case you cannot use HGT (although if would not make a lot of sense since you would probably lose several points by going away of a macroorganism).
I can see the game being slightly boring when all your bionts are "stuck" in macroorganisms, with little to do in every turn.
Actually, this happened to me yesterday by playing the solo variant, although I might be doing something wrong, because it was really weird to spend 5 turns with almost nothing to do apart of showing new events and buying again and again new organs (after they died because of the events) for the only living organism I had...until the end of the game (I had two of my bionts on my organism, and the other (unsuccesfully) trying to create new bacteria in almost dead refugia).
An important rule that we missed in our first game is that Bionts in other player's organisms can spend that player's catalysts to buy mutations. It may slightly improve the organism but allows you to interfere with their economy and potentially buy a mutation with HGT to get your Biont out.
So, while there may be players who have less control than others, no-one should be stuck with nothing to do for very long.