Also you're making it out like alakazam is some great staller that you send out once and don't switch out for a very long time...
snorlax doesn't need to switch in anyway, its perfectly fine staying in its pokeball until lategame.
the point is nobody is going to switch physical attackers like snorlax into reflect zam when they have a psychic type.
An early Zam will ALWAYS lead to Chansey being brought out (or Zam dittos I guess). The main gain of this for Zam is to lower Chansey's special and then paralyse on the switch. Sure, after that you could SToss their Starmie/whatever for a neat 100 damage, but really I'd switch out before then because waiting that long is just easting up your Psychic PP.
also, again as i've already said, there's only like a 56% chance sleep powder/lovely kiss connects after paralysis, and that's EVERY turn, not just the first turn... they're about as likely to hit you as if they'd been using sing. aside from that, if you are leading with zam, there's a good chance you'll be asleep all game and it doesn't matter what 4th move you'd used at all, but at least seismic toss lets you tack on some damage, or on somewhat rare occasions allows you to force the opponent out without sleeping you at all. basically, if you're leading zam, there's not much reason to use reflect, and if you're using reflect you might as well lead something else...
seismic toss zam doesn't need to worry about status as much because it has a different role, and because it doesn't mind paralysis as much, it thus makes a good status absorber! reflect is much less useful if you get paralyzed (i'll say it again in so you can't ignore it) because you can't go first against physical attackers or exploders or what have you (and please keep in mind setting it up against special attackers is only a feasible point if starmie, slowbro, rest jynx, and enemy alakazam are all dead, and if chansey is alive, restless jynx and exeggutor must be dead too.) but seismic toss doesn't lose any usefulness when you get paralyzed. seismic toss doesn't beat physical attackers, but it makes you less vulnerable to slowbro, starmie, and so on.
if seismic toss were as bad as you are making it sound none of these good players would be using it at all so maybe you should try either using it for yourself or being reasonable for a change of pace.