This has been said already:
Add TABS to all places and make all different heroes available at all times.
What is it about "instant gratification" that Lilith don't get? Netflix = instant access to all series, Spotify = Instant access to all songs, Google = Instant access to "knowledge".. I could go on here, but you get the point.
You listed forms of media/information that are enjoyed or used passively aka watching, listening, or reading. Gaming is a more complex activity that also must abide by different rules. This comparison is not only wrong but also stupid in essence. Do you want to watch a movie or a TV series with spoilers for its entirety revealed in the first 60 seconds? You know need to have access to all the information about what your watching right?
That aside I'm a much bigger supporter of adding a new shop for prophecy pool where in addition to the current drops you will also receive points to spend based on the difficulty and star rating on completion. To not go way overboard with "non money making content" the highest lvl difficulty when 3 stared could give 500 points per run for a total of 1000 points for those that can manage to 3 star the lvl 100 bosses without using the mercanery camp. The very first difficulty could give 125 points for a total of 250 per day. So you start of getting a maximum of 5 soulstones every 2 days to getting 10 everyday at max lvl. Every single star could be worth 33% of the points generated. So if a lvl 100 player on max difficulty gets 2 stars and then 1 start he will receive 500 points for that day. This would also give incentive to do lower difficulty bosses for those not confident of getting 3 stars since 3 star completion on tier 6 or 7 would give a lot more points then getting a 1 star kill on a tier 8. The downside being that you get less loot because of the downgraded difficulty thus presenting an opportunity cost.
The heroes added to this shop could be the oldest heroes from all other shops that would be removed to make room for new additions. This way an additional store would not have much of any impact on the access or the inflow of soulstones for new hero additions so the incentive to spend money on the game would not be diminished.
The new store would most likely make marginal difference for high lvl players since those heroes would most likely be at 7 stars already while new players would have another source of soulstones for older heroes that are no longer part of the core set.