It would be such a better idea if we could start an any tier we chose - sure, we would lose the points & rewards from the lower tiers of course - but the main reason I don’t ever bother with it, is because slogging the way through the first 3/4 is nothing more than a tedious grind. And lets face it, canning your way through with refills which are very rarely given away for free (i.e. $copely $£€) is the only way past it.
the latter stages are quite enjoyable - 25-50 levels where you really need to think about your team makeup. Such a shame you need to auto x8, wait, auto x8, wait… so many times before it become anything like fun. Given that it is supposed to be a game?!
So - I suggest you can enter SR tourneys at any tier, being able to start any tier at any time.
Risk Vs Reward also becomes more of a thing then - do you use your best toons to get one more level on legendary, or just fall back and work your way through bronze for those points?
payers will still pay to clear the lot, non-payers may be more inclined to buy the odd refill to finish a higher level rather than getting pi$$ed off after 75 auto-complete level boredom.