If you plan to live on 2.5% from 60% of your assets now, that translates to a withdrawal rate from the portfolio of 1.5%. This is such a small rate of withdrawal that you could invest just about any way you want with great security and very high likelihood you will die with far more wealth in hand than you have now. The analysis behind this conclusion is not, however, based on assumptions about what the current yield will give you or what increases in rates will do to benefit you in the future and without considering inflation. The analysis is that people have looked at how portfolios evolve under different rates of withdrawal for different asset allocations, which is what the calculators and projections you have consulted are saying.
I think it would also be better not to think about "sustainable survival income" but rather about what you think you will actually spend with a contingency added and see what withdrawal rate you get from that.