Admittedly he would've has size issues when the UFC came around cause even Royce Gracie was larger then him.
If we're talking Bruce Lee in UFC 1, this is essentially what we're talking about:-
Bruce Lee had no grappling experience. So "rolling with Gene LePell" once doesn't stop him from being tapped within the first 2 minutes by Royce or Shamrock. Jason DeLucia's track record is sort of proven since UFC so I'd say his grappling calibre was high enough too,
So let's talk strikers.
Gerard Gordeau, a Dutch Karate World Champ for 7 years and a European and World Savate Champ before the event. Wikipedia seems to say he had 31 fights on record before the event.
Kevin Rosier, a multiple time world kickboxing champion with a couple of professional boxing fights to his name.
Patrick Smith, wikipedia bills his kickboxing record at 65-4 prior to UFC 1.
Art Jimmerson, professional boxer with a record of 29-5
Zane Frazier, national karate and kickboxing champion as well as world karate champion.
Trent Jenkins, no idea.
Teila Tuli, sure Bruce would have likely beat him probably maybe.
But outside of Jenkins and Tuli, and the grapplers who would have likely won and submitted him quickly...who exactly are we saying Bruce Lee was a better striker than?