I cant dispute that one bit. It is a valid concern and one I hope they clear up quickly.
My thinking is that I don't feel the team behind Steem-Engine is going to be naive enough to put an outrageous inflation rate on it. I do not see it being any higher than STEEM which is up there according to many.
Of course, the point with inflation is how much of the tokens end up getting scooped up. I think we are both in agreement that SP is going to become scarce at some point simply with larger numbers of users. That will make the inflation rate moot.
If we see something similar with ENG, a robust market with a lot of activity, then the rate will be fine. Of course, if not, the token will be sunk.
I guess it all comes down to the risk one is willing to assume.