Bike Limiting Passion?

Yes & No

Sure some light fancy bikes can make it easier for you to do some areas of mtb, but the bike is not necessarily going to make you a better rider.

Fancy light bikes are nice of course, but the best way to get stronger and confident on the bike is to ride your entry level for a while. It's heavier yes, but it WILL make you stronger because of it.
You will learn skills that you might get too slack on if you have 5 inches of travel and the bike does all the work for you. You have to really pick your lines...less room for error.

If you can ride an entry level bike, you will find you can hop on just about any bike and make it shine. If you start on a super light fancy bike (even if you can afford it), your skills will never develop the same way as someone who starts on something entry level.
Ask anyone who got into this sport if they feel that their first POS bike taught them bike handling skills and they'll agree wholeheartedly.

If you really want to make the existing bike lighter, make it a single speed. It won't cost much, and will guarantee to make you stronger and the bike may even lose a few POUNDS.

Good Luck.

I recently upgraded from a very entry level fs bike to a used bullit, and I gotta say after two months of riding it I am easily twice the rider I was before.

There are several factors here.

1. Wanting to justify a large purchase really gets you out on the bike. The more you ride the better you get.

2. the urge to "see what this baby can do" causes you to push your limits in all directions whether climbing you a$$ off on that lightweight climbing machine or seeing how big of hit those extra inches of travel can handle. This phase leads to factor 3

3. Confidence. As good as you can ride on entry level, a good bike should (if its the right bike for you) have higher levels of comfort, durability, agility, etc, all these add up to higher limits to what you can accomplish. When you do that thing that used to kicked your ass or sketch you out on the old bike and find it easier or less scary your psychological boundaries expand and you hit it harder, faster, and ultimately funner next time.

I suggest looking for a high end used frame for a good price and throw all your salvageable parts on it. You can upgrade parts as your bike and riding style tell you what it needs. Building a bike yourself really gives you a better understanding of what you bike is made of and why it does the things it does. This knowledge helps you speak your bikes language on the trail.