The Ninja Tower can be completed even with a small set of carefully chosen S1 4* heroes. I intend to do a thorough video completing the next Tower with nothing but S1 3* and 4* s. Of course it will require items like tornadoes, but again - only Forge items are required, no Lodge heavy weaponry. And it’s important to be completed, because emblems on 4*s are extremely important if you are f2p. Plus it gives free xp - free, because it doesn’t require World Energy.
I felt the same as you about the Mythic Titan, until I realized that it is required to just reach top 10% for the more important rewards - at that stage you get guaranteed two 3* ascension mats. Of course, most of the time they can be farmables, but still. And for that you don’t need any broken heroes. Sure, elemental def down helps, but vs Hades my alt account did more damage to it with only a 4-1 yellow-Tiburtus team, no Wu Kong, no elemental def down either. Sadly without Scrolls of Alteration the top 10% seems like a distant goal, which means that you should hoard these from free sources (they are given as free prizes from seasonal events or Path of Valor on occasion) and use them only vs the Mythic titan. And of course, develop your base to the point where you can produce them. And if you are in alliance that has a lot of p2p players, they will most definitely buy the Mythic Titan bundle, supplying you with enough Alteration scrolls for one big hit.
No one in the top places of the Starfall event had a Starfall hero. Most even used heroes like cGunnar even on Legendary just to further improve their scores. Here the real issue is the willingness of certain players to waste ton of money for unlimited replays of stages until they get that 0.00001% perfect board. This seems really sad, doesn’t show any real skill IMO but is of course encouraged and made that way by the developers to syphon most money from the players in the form of refill gems. But this is in every challenge event - not only Starfall. Can’t compete with that unless you are willing to do the same. And it’s really best to settle for top 1k, but at some time probably even that will become very hard to attain, since more and more players will be willing to waste ton of money just to get to the top. Overcompensating, maybe. I see no other reason for them to do it…
Been there done that. Climbed to Diamond thrice with only a very limited roster of 4*s. Opened some Diamond chests. Found the usual crap inside - nothing special. Had to fight constantly premium A+ defences against the odds. No fun. Dropped back to platinum. And in Platinum I can fill raid chests regularly with 8-10 raids max, and the loot seems to be the same - yesterday pulled Rings from Platinum raid chest, so it’s fine actually. Better to fill it in Platinum fast than in Diamond slow and get frustrated from the power creep at the same time.