Edit in JSFiddle

var $slides = $('.swiper-slide');
var duration = .5;

var swiper = new Swiper('.swiper-container',{

  direction:'vertical',
  autoHeight: true,
  slidesPerView: 'auto',
  resitance: true,
  resitanceRatio: 0,
  watchSlidesProgress : true,
  virtualTranslate : true,
  on:{
    activeIndexChange: function(){
      var swiper = this;
      
      if(this.activeIndex){
        //...something
      }
      
      this.update();
      
      if(this.slides.length - 1 == (this.activeIndex + 1)){
        gsap.to($slides.not('.swiper-slide-active, .swiper-slide-next'), {opacity:0, duration:0, delay: .5});
      }
      else{
        $slides.css('opacity',1);
      }
      
    },
    setTranslate: function(translate){
      var swiper = this;
      var slides = swiper.slides;
      var $slide;
      var progress;
      var scale;
      var translate = swiper.getTranslate();
      
      for(var i=0; i < slides.length; i++ ){
        $slide = slides.eq(i);
        progress = Math.max(Math.min($slide[0].progress, 1), -1);
        scale = Math.max(1 - Math.abs($slide[0].progress), 0.75);
        
        if(progress > 0){
           //if($slide.data('scale') === 'true' ){
           if($slide.hasClass('data-scale') ){
           
            gsap.to($slide, { transform: `translateY(${ -swiper.slidesGrid[i] }px) scale(${ scale })`, duration: duration});
          }
          else{
            gsap.to($slide, { transform: `translateY(${ translate }px) scale(${ 1 })`, duration: duration});
          }        	 
        }
        else{
          gsap.to($slide, { transform: `translateY(${ translate }px) scale(${ 1 })`, duration: duration});
        }
      }
  
    }
  }

});

<div class="contents">
  <div class="swiper-container">
    <div class="swiper-wrapper">
      <div class="swiper-slide data-scale" ><div>slide 01</div></div>
      <div class="swiper-slide data-scale"><div>slide 2</div></div>
      <div class="swiper-slide data-scale"><div>slide 3</div></div>
      <div class="swiper-slide" ><div>크기 안줄어듬</div></div>
      <div class="swiper-slide" ><div>크기 안줄어듬</div></div>
    </div>
  </div>
  
</div>

.contents{
  height: 100vh;
  
}
.swiper-container{
  height: 100vh;
}
.swiper-slide{
  padding-bottom:24px;
}
.swiper-slide > div{
  display:flex;
  align-items: center;
  justify-content: center;
  height:300px;
  padding:24px 0;
  transform-origin: 50% 0;
  border-radius: 10px;
  background:#eee;
  box-sizing: border-box;
}