If by two-tier, you refer to the prosecution (i.e. drafting) vs. litigation (i.e. lawsuit) tiers, there is a clear separation in the industry. I do prosecution exclusively, and can't answer if it is inherently desirable (inasmuch as any career path is desirable), but I don't find litigation appealing. On the litigation side of the world, you might find a faster-paced, higher-stressed, higher-compensated environment which has more significant deadlines and "stakes" especially when involved in court proceedings. However, I would also imagine that a more flexible career path is tied to such work since litigation can translate broadly to other lawyerly endeavors vs. the more specialized prosecution.
But, to stress again, the work is inherently different on prosecution vs. litigation. Prosecution also has its work deadlines, but these can be managed more flexibly in practice. Prosecution is a joy for someone like me who prefers to largely work independently (once you learn your craft sufficiently), attempt a good work-life balance, learn new tech every day, apply that knowledge to writing about it in a very specialized manner, compartmentalize tasks (each patent can have its own mental silo), and still do some limited "lawyerly" work dealing with examiners at patent office to attempt to get patents allowed in light of the prior art. Plus, depending on the firm and your ambition, you can branch into anything - litigation, licensing, contracts, etc.
I should note that you don't need to pass the patent bar exam to do litigation, but you would eventually need that for prosecution (agent, attorney). So some say that it can be harder to switch from litigation to prosecution because of that barrier.
But, to stress again, the work is inherently different on prosecution vs. litigation. Prosecution also has its work deadlines, but these can be managed more flexibly in practice. Prosecution is a joy for someone like me who prefers to largely work independently (once you learn your craft sufficiently), attempt a good work-life balance, learn new tech every day, apply that knowledge to writing about it in a very specialized manner, compartmentalize tasks (each patent can have its own mental silo), and still do some limited "lawyerly" work dealing with examiners at patent office to attempt to get patents allowed in light of the prior art. Plus, depending on the firm and your ambition, you can branch into anything - litigation, licensing, contracts, etc.
I should note that you don't need to pass the patent bar exam to do litigation, but you would eventually need that for prosecution (agent, attorney). So some say that it can be harder to switch from litigation to prosecution because of that barrier.