How much stronger would recent middleweight and light heavyweight history be….?

Yes they've done damage like all tweeners. Its hard to say because with division hopping the fighters SMW is "stealing" typically fight in MW or LHW just for shorter. Hearns, Barkley, Calzaghe, Ward and Canelo were all LHW champs but because of SMW they were only in the division briefly. Someone like a Nunn or Abraham might have stayed at MW. RJJ might have stayed at MW a little bit longer.

The effect depends on the situation.I think the last few years 168 has been doing more damage than normal with Canelo, Plant, Benavidez and Morrell. LHW and MWs had some of its best eras the past 40 years and some bad lulls.

 

I think it would have been much better. 168 has diluted the strength of both 160 and 175.

 

the old way, was obviously more of a natural transition for ALL Weights.

as fighters got older and grew out of a Division, damn near every fighter in history (except proper Big fellas, who were simply just HW's), was a 'something or other' cum the next Division up, i.e MW cum L-HW...

Less weights and BUSIER fight schedules ensured fighters fought in & around their Own Weights & Stature/size... very few Bigger men exploited to fight down contrary to their Natural Stature back then.

In fact, that would be a good Thread - Past Fighters that Fought DOWN lighter than their 'true weights' ?

the only one I can think of that saw the niche and employed it was the Scot's Flyweight Tancy Lee, who was really a Bantam cum Featherweight, who sought out Flyweight status first to insure his notoriety...

he was doing 'then' what all fighters do today.

 

Yes definitely fighters like Eubank, Calzaghe, could easily make Light Heavyweight Calzaghe himself said he struggled making the Super Middleweight limit for years.

Just imagine we could've had Calzaghe fighting the likes of a prime RJJ.