I told you my opinion, keep the jardini. In a couple years if you couldn't care less for the well being of the jardini, you will keep it crammed in that tank of yours. Otherwise you'll then see the tank is to small and will find other housing options.
As for the silvers in the 55g. You really think it's right justifying your wrong doing by comparing to others wrong doings?
BTW your trusted LFS main goal is to sell you fish, food, etc. So most will just tell you what you want to hear. Simply put a 30" long fish will not do well in a 22" wide tank.