It could be argued that unless you have 500 hours RHS time you don't need an ATPL!
That's a funny way to look at it, yes
However I think there are exceptions. Recently I was fortunate to be able to fly a TBM850 (with a factory instructor) and in researching the necessary pilot qualifications it turned out that an ICAO ATPL (which includes the otherwise not very useful FAA single engine ATPL) can serve as one of the necessary qualifications. So, building 1500hrs in a Cessna 150 and getting the FAA ATPL is not totally useless and could actually be quite useful one day, though not in any airline pilot context.
Pilot Qualifications
US registered aircraft No Type Rating is required because the TBM is below 12500lb and is not a turbo
jet. There is a "High Altitude Endorsement" ground course with 1 flight to simulate explosive depressurisation and oxygen mask use, etc.
FAA prerequisites are: PPL, CPL or ATPL. To be PIC of N-reg TBM you need three endorsements, all of which can be issued by any FAA instructor: High Altitude (all aircraft certified above FL250), High Performance (all aircraft with more than 200 HP per engine), and Complex (all aircraft with retractable gear).
EASA registered aircraft In EASA-land, no Type Rating is required but there is a Class Rating called: "Aerospatiale S.E.T." (the name will soon be changed to "Aerospatiale TBM").
The Class rating is valid for 2 years and it is mandatory to pass a Class Rating proficiency check to renew the Class Rating every 2 years. This Class Rating can be done by a Class Rating Instructor (CRI); it is not mandatory to do it in a Flight Training Organisation (FTO). After the training, the Check Ride will be done by a Class Rating Examiner (CRE).
JAA prerequisites are: PPL, CPL or ATPL, and an "HPA" (High Performance Airplane") course certificate (which is not needed if one has passed the ATPL exams or holds any ICAO ATPL). The "HPA" course must be done in a Flight Training Organisation (FTO).