I tend to agree with you. The challenge festival doesn’t dilute the pulls with season 1 heroes. I’d pull there for sure. I’d pull now but I’m at 100 on my fated summons and waiting for the next heroes to be available.
Assuming that you have sufficient roster space (need gems for that).
Generally you go for the portals with no Season 1 heroes: Summer Solstice, Black Friday, Challenge Festivals I and II.
But, I’ll mention that many of the base Challenge Festival I are available in the Hero Academy levels 5 (3*), and 8 (4*). So if you can wait until then, you don’t risk “wasting” your gems.
As well, for CFII, you can save up your challenge tokens and only use them during CFII which will give you an opportunity for “free” pulls.
Some will say costume chamber, but I’d say no because there are many free costume keys so you have a good opportunity for free pulls there.
However, for Summer Solstice and Black Friday, all you can use are gems. So I would say these two would be the best, and then CFII.
Personally, I save up all my gems and spend it only on roster expansion and Summer Solstice / Black Friday 30x summons. I did one 30x Summons on each of the three last Summer Solstice / Black Friday events (so since 2021 BF, maybe done so on 2020 BF too) and it gave me a great deal of new heroes on every rarity. Sure they were some duplicates but if you already have some of the CF heroes, the CF summons aren’t as worthy anymore because the chances of duplicates goes up quickly although on SS/BF, the pool is so wide and keeps expending every time that chances of getting a duplicate stay pretty low. Also the variety is good rather than spending your hard-earned gems on a particular summon portal.
A problem with this is, in part, once you have pulled at this portal enough to have all (or nearly) all the 3* and 4* heroes from this portal — not that hard a feat, since there aren’t that many different ones — then there’s not that much of a distinction between “season 1 heroes” and “duplicate CFII heroes.”
which is what I’ve been wondering about myself. (Plus, with the latest blatant aether cash grab, “just wait” is sounding better and better.)
I save my gems for solstice, Black Friday, or challenge festival portals. As much as one good hero can upgrade my roster, getting ten usable heroes has been helpful.