This idea that Riley lacks bat speed is a myth that has been perpetuated by Keith Law, and he will not let go of the fact that he is dead wrong about Austin Riley. His actions at 3B are better than most people felt, and he has a rifle for an arm. This is a big time power prospect who has a future in the middle of the Braves batting order.
A lot of people confuse a slow bat with a long swing. A guy can't hit a ball 400' without generating a lot of bat speed, but a guy can have a long swing like Frenchy did and cause him lots of issues.
I couldn't see anything wrong with Rileys swing, but he only swung at 1 fastball and a bunch of loopy curves. He does look noticeably more fit, and that is not a trivial thing.
I consider Longenhagen the premier prospect guy in the public sphere. He sees more talent live in a single day than the other prospect writers see in a month. He is around more scouts on a daily basis than any other writer on the planet. He says Riley's bat speed is fine, but he is going to have to play 1B which will put too much pressure on the bat and the package won't play for a contender.
BA is getting this crazy idea that Riley is good defensively somewhere, so I would trade Riley to the team that values him as a plus defensive 3b.