Pack weight from TOTS

I believe the pack system is based on specific weightings assigned to each card, not just a simple 1-in-X chance. So, if there are 52 cards available, you don’t have an equal 1/52 chance of pulling any of them. Each card has its own drop rate or weight. Generally, the higher-rated or more valuable a card is on the market, the lower its probability of being pulled.

A good comparison would be with Pokémon cards. When the original sets were released, a common card like Caterpie might have had a 50%+ chance of appearing, while a rare card like Charizard might have had a drop rate below 3%. You can also visualize this like a spinning wheel: the lower-rated cards take up large sections of the wheel, while rare cards occupy small, thin slices. You can still land on those rare slices, but you're much more likely to hit the bigger sections — which is why so many players end up packing the same, less desirable promo cards (like Nedved, as you mentioned).

I personally feel EA should disclose the exact odds of pulling individual cards. Currently, they only provide probabilities based on rating thresholds (like 88+ rated) or promo categories (like TOTS). They also include vague disclaimers such as:
“Specific pack content is randomly selected from large groups of available items. The probability of receiving any particular item within the stated range or type may vary. Because of the large number of available player items, the probability of receiving any individual player item is significantly less than the displayed probability for the OVR or special category range and is often <1%.”

Take the example of trying to pack TOTS Cole Palmer. If you open the "Essential TOTS (Week 2)" pack, which gives you a 23% chance of pulling any TOTS player, and within that the chance of getting Cole Palmer is 0.01%, your actual odds per pack are just 0.0023%. That’s extremely low, and this is the kind of number that should be clearly displayed. In my opinion, transparency about exact player-specific odds would be a big improvement over just showing broad category percentages.