Psylocke can't be affected by any genetic or molecular manipulation by Rachel, but she can still get smashed around and get killed the old fashioned way. Psylocke is a powerful telekinetic, but she is notoriously known for using any psi power she has to augment he "ninja" skills. Rachel uses her tk primarily for long range attack, and is a lot more talented at using her power creatively(like suffocating the Blob.) They haven't placed a limit on what Psylocke can do, and they haven't done that to Rachel either, yet Rachel has been shown to be a lot more versatile.
when did rachel say psylocke was more powerful? and since when is she more experienced, Psylocke is little more than a psychic brawler. When her tk first manifested she couldn't even lift a dime, and i haven't seen anything to assume she has gained the kind of fine control Rachel has. Rachel has been using tk a lot longer and has shown to be much more versatile even without trying (altering her genome). And if Rachel is anything like the rest of her family she probably has all kinds of mental blocks due one form of trauma or another.