The problem was full power 10mm is a lot and as Hilton Yam stated ina. Video (link below) nobody is gonna like shooting it in a 1,000 round 2 day class. AND the size and weight of the gun makes it not user friendly unless you have large hands.
I was around in LE when 10mm came out and a couple agemcies in Montana did Glock 29’s (I think Yellowstone County might still run it)
What many have learned while the 357 is a great round many agencies (Indianapolis PD used 125 SJHP) had great success with both 2 1/2” amd 4” that 125 grain 357 was doing 1,400-1,450 in 4” and about 1,200 in 2 1/2”. The shootings with the 2 1/2” was just as effective.
So a good quality 9mm 124 gr JHP runs 1,200 FPS there is no reduction in stopping power shot for shot in the same place. You’re just giving up the blast to get there.
Look at all the main duty rounds 124 Gold Dot and HST or 135 Critical Duty they are all dropping bad guys from agemcies that use them. Indy OD uses 124 HST and they have a whole YouTube channel they post their shootings on you can see how well it works (IMPDTV)
Hilton Yam touches on the 10mm at the 9:18 mark but the whole video is pretty good on the Miami FBI shooting most here will find interesting. Always liked Mr Yam’s 10-8 channel and how he explaines stuff. Class act