Sorry for the slow response. Being away for a week has let ALOT of small chores build up.
A Trane unit properly installed should give you 20+ years. No ifs, ands. or butts. So, somewhere a part is failing. If you've lost freon two years in a row, well they need to find the leak. "Time to start looking at a new unit" - yeah, that's "I'm a lazy technician and don't want to work the job, plus I get a commission on every new unit I sell". Were there systems that had leaks that I couldn't find. Sure. But I'd say 90%+ I'd find the leak but the customer didn't want to pay for the repair. That's a big outlay of cash money TODAY - would much rather credit card it and pay it off over years.
Stick with your R22 unit. The powers that be are planning on banning R410a with 5-6 years, forcing everybody to switch freons AGAIN. If you keep the R22 you'll only have to convert once, rather than twice by doing R410a and then R-32.
They "coincidentally" no longer carry Trane, but Carrier. Translation: Trane is an expensive unit. Carrier is much cheaper. Therefore, there's more profit in selling Carrier, because you can bet your bottom dollar the price they're charging for installation ain't gonna come down. Also, it might be they've switched brands because they've been having problems like yours with alot of customers, and those customers have griped to the manufacturer. Trane is tightening the screws on the companies warranty claims, and so they've decided to switch.
But honestly, if the units leaking, that's why the performance is suffering. They need to find the leak and fix it. Remember too that when refrigerant leaks it's not only losing freon but also oil (entrained in the freon as a vapor). When they top the charge off they're putting in virgin freon. No oil. Thus over time an unrepaired leak will allow the system to lose enough oil to seize the compressor, which will probably make you change the system.
They should drain the freon, cut and seal the system into 3 parts (condensing unit, evaporator coil, and the lineset between). Pressurize with dry nitrogen to 400 PSI, leave it for a few days. Slap a gauge onto each section, see which one has lost pressure. Then they can narrow down the spot or component that's bad. Alot of work, I used to charge $400 to do that. But many companies don't want to piddle around with small change repairs, instead opting for the big buck installs.