/SMN wasn't necessarily a bad choice, but citing max MP as the reason for choosing it shows to me they missed the mark.
To be fair, the mark kind of sucked regardless of how you chose it. Before /SCH and level cap increased /RDM, WHM had terrible subjob options. /SMN offered higher MP, 1/tic refresh, and a carby that was very VERY occasionally useful as a distraction. Oh, and there were those awful days of Aerial Armor rotations on PLDs for tanking sky gods and stuff. Good times, good times.
Personally, I was more of an action WHM, so I needed /BLM most times. Some **** fool would get killed in sky and I wouldn't have much chance of getting them out without tractor and elemental seal sleepga. Warp was also nice. I never paid Conserve MP much mind and I'm pretty convinced it never cared about me either.
Back on topic, I see a lot of melees go /BLM for the MAB when they brew using elemental weaponskills. To me that feels sort of like attaching a sharp stick to an ICBM so you may impale something before it blows up, but I guess with brews you want every advantage you can get.