These are the numbers I found for 5th and 6th gen games:
FFVII: 10.0
FFVIII: 8.6
FFX: 8.5 Ocarina of Time: 7.60
Wind Waker: 6.79
Majora's Mask: 6.82
FFIX: 5.5
FFX-2: 5.4 Oracle of Seasons & Oracle of Ages: 3.99
Minish Cap: 1.76
So maybe "a lot" is an overstatement, but they did generally sell more. You have a point regarding sales-per-console, but also remember PS1 had over 1900 games to N64s 388. That's way more competition for third party FF games to get sales. Many people that buy Sony consoles don't even look twice at JRPGs, whereas most people that buy Nintendo consoles know day one they are going to get the latest Mario and Zelda.