Several years ago I would have agreed with you, but right now, D-1 has talent from top to bottom. It's not like the old days, when there were two or three tiers, and programs like last-year's D-1 runner-up Quinnipiac were de-facto D-3 teams.
As far as the direct comparisons go, there aren't really any, but watch how the US-Under 18 team hammers a good D-3 team on a given night, then goes on to be buried by a very pedestrian D-1 team a night or two later... Additionally, one could consider how dominant a good many D-1 transfers are at the D-3 level, when they shined the pine at their mediocre D-1 schools. (Which, of course, was why they transferred to D-3 in the first place: for the ice-time.)
I've done a (very) little research lately regarding the DOBs of D-3 guys, and it seems that the most successful teams are often stocked with overage players who went un-drafted... And, if you're un-drafted at age 23-26, there's probably a good reason for it.
My theory is that the scouting has gotten so much more efficient at both levels that guys generally land where they belong, and the proof is in the pudding: D-3 guys almost never ascend to an NHL job, while that league is loaded with D-1 players, some of them among the best in the league... I'll even go so far as to predict that if my beloved Utica team -which I expect to contend for an D-3 NC this year, if they stay healthy- would likely go winless in Hockey East.
The D-1/D-3 comparison seems to be between apples and oranges these days, IMO.