Vouchers will be fungible and can be bought from external markets. So smart people won't stake SPS just to buy a CL pack. They would rather buy the Voucher from external market.

Also note that the sps you you stake also gives you daily staking rewards and possibly more benefits in future. So staked SPS is not wasted but can be unlocked and sold. Longterm hodlers would prefer staking for additional benefits.

So it's all on people what path they choose.

Without the voucher system only whales would get most of packs in presale. No fish would have the chance.