Considering being good at putting is relative to one being bad at putting, doesn't the question center around how difficult it would be for the good putter and bad putter to adjust to the new weight ball?
I'm not talking about adjusting. I'm talking about how a lighter ball would actually behave when putted.
A lighter ball would be more affected by little imperfections and would bounce around more. Randomness levels the playing field and favors "bad" putters over good putters. The more "luck" plays a role, the less important "skill" becomes.
That sounds like it would fall under the definition of "Rub of the Green". Any impact a green may have to a lighter ball would be equally experiences by all players.
Randomness is good in golf. It is what creates interest. If we knew exactly where each shot was going to go before we hit it we wouldn't play. We accept the impact of randomness in all aspects of play, both positive and negative. We expect the way we play to be influenced by randomness, as we try as much as possible to control it.
This is where skill comes into the equation. Luck, as the manifestation of randomness, does not diminish the importance of skill, in fact is it the exact opposite. As randomness is heightened, skill and strategy is heightened in turn. If you believe randomness can level a playing field, it should be easy to also see that same randomness is better for identifying great skill. As great skill will rise above the effects of randomness across a field of players. Negating the bad and accentuating the good.
Greens have not been smooth and flat for long. Probably a shorter amount of time than the 1.62" ball has been banned. Yet, for the entire history of the game there have been players that have been identified as great putters. Putting on bumpy greens, players like Locke, Crenshaw, Nicklaus, Casper, Jones, & Travis were still able to unquestionably separate themselves from the rest.