The system is very clear and the first explanation you received was wrong, If the 280 PlusPoints are not earned natively, then in January (not February) of the next year, as a LT 1K or GS, you will received 280 PlusPoints. There are no extra PlusPoints for being a GS over being 1K. Regular GS, due to spending more, tend to have more PlusPoints but even in LT status, PlusPoints beyond 280 is dependent on spend, The first explanation was wrong and the system was worked this way since the certation of LT GS.

LT status for all level has been a "floor", at guarantee of not less then a certain level of benefits. Many have asked if LT status is a new starting point and if have LT Gold, if you then have a high initial starting point and early to ear 1K or Plat and no that is not true. We all fall back to zero each year. Your "disincentive to travel" applies at all levels, but if you don't travel you don't get to use your other GS benefits. That's the incentive.