Well, at WORST Reggie Lewis would've made numerous All-Star games, I believe. He also would've been a dogged defender against Michael Jordan, once blocking his shot FOUR TIMES in one game.
IIRC Reggie ALSO scored 30 points in that same game, along with Larry.
As for Bias?
https://www.youtube.com/watch?v=ZqvUeJnDtOQWe unfortunately will NEVER know for sure how good Bias would've been but Larry Legend would've exited EARLY if he remained alive.
I think that says a lot.
Now "IF" Larry Legend retires in 1988, then we do not get THIS

Could Bias have taken Larry's place? As good as I believe Bias "Would've" been I doubt he'd be THAT GOOD to make Team USA and sit next to Michael and Magic in four years time...he'd probably be in his Prime Years by 93-97....
I'm not sure how good the REMAINDER of a Reggie-Lenny team would've been...Chief was on his way to retirement, McHale was on bad wheels by 1987 and Bill Walton - bless his heart - was ONLY great for us in 1986.
Dennis Johnson was getting older...who would've replaced him at PG? And what about Danny? Reggie played the same spot as him...
Fast forward to NOW? I see greatness in JB and Jayson. They DO remind me of the "Could've Would've Should'ves" of Reggie-Lenny.
They ALSO have a BETTER team around them going forward, with Gordon Hayward, Smart, Theis and Kemba.
Kemba Walker and GH have been All-Stars and GH is just about back to his 2016-17 levels.
Bias was dominating in College before we drafted him...Tatum? While a great player for Duke I don't think he had QUITE the buzz coming out as Bias did...but it was close.
In short I see a wider window of banners for JB and Jayson, with the talent level between the twosomes being VERY close..
Lewis and Lenny would've had to depend on Red do some miracle manuevering to get a good PF, C and PG to replace DJ, Chief and McHale....this would be daunting, I'd guess.

Loving things going forward for BOS.
Keep Hayward, get Kemba healthy and just let Marcus run loose and we have just about as good a shot as ANY team currently.
EDIT - I voted Jaylen and Jayson going forward.