Tiedemann is a good prospect don't get me wrong, but he's still got a lot to prove. His professional league track record is also really small (18 starts and 78.2 IP professionally).
But there's literally dozens of pitching prospects that can touch 97-99 mph in the minors, many of them haven't panned out. For every one arm that pans out, dozens don't.
There's only a handful of real aces in the MLB, just based on 2022 season these pitchers had over 4.5 fWAR and 160+ IP
(If your ace can't even stay on the mound for most of the season it's not a true #1, I expect an Ace to compete for Cy Young)
6.3 Aaron Nola - 205 IP
6.2 Carlos Rodón - 178 IP
6.1 Justin Verlander - 175 IP *AL Cy Young
5.7 Sandy Alcantara - 228.2 IP (jesus) *NL Cy Young
5.7 Kevin Gausman - 174.2 IP
5.6 Ohtani (+3.8 batting fWAR) - 166 IP
5.0 Max Fried - 185.1 IP
4.9 Shane Bieber - 200 IP
4.6 Corbin Burnes - 202 IP
4.4 Dylan Cease - 184 IP
4.4 Framber Valdez - 201.1 IP
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4.1 Alek Manoah 196.2 IP
A more recent success story would be Shane McClanahan who pitched to 3.5 fWAR and 166.1 IP in 2022. Lefty with stuff similar to Tiedemann.
It's debatable if McClanahan is a legit ace, but it'd probably would be best case scenario for Tiedemann until we see more of him.
In term of lefties, some of the best performances in 2022 were:
6.2 fWAR Carlos Rodón
5.0 fWAR Max Fried
4.4 fWAR Framber Valdez
4.0 fWAR Tyler Anderson
3.8 fWAR Martin Pérez
3.6 fWAR Nestor Cortes
3.5 fWAR Shane McClanahan
3.2 fWAR Julio Urías
The highest octane fastball here would be McClanahan's 4 seamer that averages 96.7 MPH and Rodon's 4 seamer at 95.5 MPH.
The rest of the group are closer to 91-94. Stuff helps a lot, but so does movement, location, extension, spin, sequencing, pitch mix, etc.
This all bakes into swinging strikes, contact rate, groundball rate, ability to reduce hard contact and barrels, etc. Pitching is complicated.
Wish we can just look at a pitcher's fastball velo and go YOLO in determining their upside.
Tiedemann is an exciting prospect and trending up, but need to see more of him.