As for future-proofing lens for body upgrade, you are probably thinking too much. If you spend the extra money for FF lens on crop body, u are not fully utilising the money spent. You think it will be a savings in the long term, how about considering it a larger opportunity cost at the start? Smth to think about.
For body specs, all of the points u mentioned are not valid, in the sense that DSLR is not superior in those aspects mentioned, comparing apples to apples. (Of course no mirrorless can rival D4 or 1Dx).
And for the A77, it's one of the fastest camera in terms of focusing and fps, at the point of its release. May I know the lens u are using it with? Af accuracy and speed is largely dependent on lens as well. And given that it's a company camera, it may not be maintained as well as I would expect. Lens alignment may be off, and require calibration. Do consider these factors before you pass your judgement.
Regardless of your choice of camera, it's best to have hands-on experience with them before u buy and not just rely on tech specs.