Does this mean AMD is inherently more secure?
Flaws have been found in it. They are probably not as bad as Intel.
Leaving the VISA environment accessible to ME is something that I hope AMD would never entertain out of a wealth of caution for their customers.
Not sure there's any evidence this is likely to be true - except for the fact Intel processors are widely deployed.
We would hope that their architectural restraint would extend to their SP.
It's slightly ambiguous whether you mean 'the flaws in AMD IME-near-equivalent are not as bad as the flaws in the IME' or 'AMD's IME-near-equivalent is not as bad as the IME'.
On the 2nd interpretation, it seems that AMD's 'ME' is likely not as powerful/mature as Intel's ME. On the other hand, on certain machines the IME can be disabled or largely neutralised, while I know of no such possibility for AMD.
The maturity of both platforms is opaque, varying, and the only reasonable feature that most consumers would want is an off switch.