We have a wealth of stability improvements and bug fixes which should make battles across all game modes (but especially BNW) much less problematic.
That said, while I can understand that some players are having more problems than others in those features, the structure of the game progression is intended to have those as places to specifically grind for the evo requirements to evolve characters and talismans, and them being farmable from the Campaign was merely a stop gap until the respective features became available.
Regarding the cost of the dungeons, they're priced appropriate to the rarity of the main drops in question, and the length it takes for players to clear those dungeons. We do not want players to grow even more fatigued being able to enter the highest BNW floors for 5 Sands of Time, even though battles are a magnitude (or more) longer than the campaign. The current "free entry" event aside, we want players to balance their Sands of Time expenditure across various features.
The reason there is a limit to begin with is to encourage players to branch out and buy different items that are available for Trooper Badges, especially with the exclusive fragments that will be arriving to the Trooper tab. Because of how important Skill Shards are, we don't want players to choose to not buy other items because they want to invest their Trooper Badges into Skill Shards alone (and also don't want players to just invest in souls instead of also trying to get Skill Shards), so adding limits is the most appropriate way we can do that.
That said, while this means you're getting less Skill Shards from Trooper Badges alone, that's also why we added the ability to get an additional Skill Shard each week from the Arena, and are able to get additional Skill Shards each month for Gold; we recognize these are important resources and want to ensure you have a variety of ways to get them.
Well, if you have some Eternity Souls, you may want to hold onto them for a bit longer, but I can't say much more than that.
That said, no characters are planned to be added to the Eternity Souls any time soon, but characters in the realm of "Eternals" (either actual Eternals or characters as strong as them) are planned to be added to the game outside in places that aren't the normal Rare Soul/Legendary Soul/etc availability.