If you put it favourably, it looks like Roberts has six of the 13 best seasons posted by either player (and neither of the top two).
Less favorably, he also has just six of the best 17 seasons posted by either of them.
My way of doing it mirrors your results fairly closely:
[TABLE=collapse]
[TR]
[TD]PCHA[/TD]
[TD]1920[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
22
[/TD]
[TD]
26
[/TD]
[TD]
7
[/TD]
[TD]
33
[/TD]
[TD]103[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1913[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
15
[/TD]
[TD]
24
[/TD]
[TD]
5
[/TD]
[TD]
29
[/TD]
[TD]100[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1917[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Vancouver Millionaires[/TD]
[TD]LW[/TD]
[TD]
23
[/TD]
[TD]
43
[/TD]
[TD]
10
[/TD]
[TD]
53
[/TD]
[TD]98[/TD]
[/TR]
[TR]
[TD]NHA[/TD]
[TD]1914[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Montreal Wanderers[/TD]
[TD]LW[/TD]
[TD]
20
[/TD]
[TD]
31
[/TD]
[TD]
13
[/TD]
[TD]
44
[/TD]
[TD]98[/TD]
[/TR]
[TR]
[TD]NHA[/TD]
[TD]1915[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Montreal Wanderers[/TD]
[TD]LW[/TD]
[TD]
19
[/TD]
[TD]
29
[/TD]
[TD]
5
[/TD]
[TD]
34
[/TD]
[TD]85[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1914[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
16
[/TD]
[TD]
24
[/TD]
[TD]
4
[/TD]
[TD]
28
[/TD]
[TD]80[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1912[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
16
[/TD]
[TD]
24
[/TD]
[TD]
0
[/TD]
[TD]
24
[/TD]
[TD]80[/TD]
[/TR]
[TR]
[TD]NHA[/TD]
[TD]1916[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Montreal Wanderers[/TD]
[TD]LW[/TD]
[TD]
21
[/TD]
[TD]
18
[/TD]
[TD]
7
[/TD]
[TD]
25
[/TD]
[TD]68[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1918[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Seattle Metropolitans[/TD]
[TD]LW[/TD]
[TD]
18
[/TD]
[TD]
20
[/TD]
[TD]
3
[/TD]
[TD]
23
[/TD]
[TD]66[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1922[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
24
[/TD]
[TD]
13
[/TD]
[TD]
6
[/TD]
[TD]
19
[/TD]
[TD]61[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1915[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
17
[/TD]
[TD]
17
[/TD]
[TD]
10
[/TD]
[TD]
27
[/TD]
[TD]60[/TD]
[/TR]
[TR]
[TD]NHA/CHA[/TD]
[TD]1910[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Montreal Shamrocks[/TD]
[TD]C[/TD]
[TD]
15
[/TD]
[TD]
21
[/TD]
[TD]
0
[/TD]
[TD]
21
[/TD]
[TD]60[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1920[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Vancouver Millionaires[/TD]
[TD]LW[/TD]
[TD]
22
[/TD]
[TD]
16
[/TD]
[TD]
3
[/TD]
[TD]
19
[/TD]
[TD]59[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1921[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
24
[/TD]
[TD]
9
[/TD]
[TD]
11
[/TD]
[TD]
20
[/TD]
[TD]59[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1918[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Portland Rosebuds[/TD]
[TD]C[/TD]
[TD]
18
[/TD]
[TD]
14
[/TD]
[TD]
6
[/TD]
[TD]
20
[/TD]
[TD]57[/TD]
[/TR]
[TR]
[TD]NHA[/TD]
[TD]1912[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Montreal Wanderers[/TD]
[TD]LW[/TD]
[TD]
18
[/TD]
[TD]
16
[/TD]
[TD]
1
[/TD]
[TD]
17
[/TD]
[TD]53[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1916[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Portland Rosebuds[/TD]
[TD]C[/TD]
[TD]
18
[/TD]
[TD]
14
[/TD]
[TD]
3
[/TD]
[TD]
17
[/TD]
[TD]49[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1917[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Portland Rosebuds[/TD]
[TD]C[/TD]
[TD]
24
[/TD]
[TD]
22
[/TD]
[TD]
4
[/TD]
[TD]
26
[/TD]
[TD]48[/TD]
[/TR]
[TR]
[TD]NHA/CHA[/TD]
[TD]1910[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Ottawa Senators[/TD]
[TD]LW[/TD]
[TD]
10
[/TD]
[TD]
16
[/TD]
[TD]
0
[/TD]
[TD]
16
[/TD]
[TD]46[/TD]
[/TR]
[TR]
[TD]NHA[/TD]
[TD]1913[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Montreal Wanderers[/TD]
[TD]LW[/TD]
[TD]
16
[/TD]
[TD]
17
[/TD]
[TD]
2
[/TD]
[TD]
19
[/TD]
[TD]40[/TD]
[/TR]
[TR]
[TD]NHA[/TD]
[TD]1911[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Quebec Hockey Club[/TD]
[TD]C[/TD]
[TD]
9
[/TD]
[TD]
13
[/TD]
[TD]
2
[/TD]
[TD]
15
[/TD]
[TD]38[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1919[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Aristocrats[/TD]
[TD]C[/TD]
[TD]
20
[/TD]
[TD]
5
[/TD]
[TD]
4
[/TD]
[TD]
9
[/TD]
[TD]26[/TD]
[/TR]
[TR]
[TD]WCHL[/TD]
[TD]1924[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Saskatoon Crescents[/TD]
[TD]C[/TD]
[TD]
17
[/TD]
[TD]
2
[/TD]
[TD]
1
[/TD]
[TD]
3
[/TD]
[TD]8[/TD]
[/TR]
[TR]
[TD]PCHA[/TD]
[TD]1923[/TD]
[TD][/TD]
[TD]Tommy Dunderdale[/TD]
[TD][/TD]
[TD]Victoria Cougars[/TD]
[TD]C[/TD]
[TD]
27
[/TD]
[TD]
2
[/TD]
[TD]
0
[/TD]
[TD]
2
[/TD]
[TD]4[/TD]
[/TR]
[TR]
[TD]NHA[/TD]
[TD]1911[/TD]
[TD][/TD]
[TD]Gord Roberts[/TD]
[TD][/TD]
[TD]Montreal Wanderers[/TD]
[TD]LW[/TD]
[TD]
4
[/TD]
[TD]
1
[/TD]
[TD]
0
[/TD]
[TD]
1
[/TD]
[TD]3[/TD]
[/TR]
[/TABLE]
I see that his best years were 1913 and 1920, and everything in between was relatively meh. While Roberts' best 4, and best 5 years, came in consecutive spans. Still, just like Dunderdale has a huge dropoff from 2nd best to 3rd best, Roberts' drop from 3rd to 4th best is just as much.
They are essentially equal in best 5-6 seasons. The dropoff that concerns me is Roberts' lack of anything beyond a 9th-best season. Dunderdale did the same in his 12th-best season (in just 9 games of a 16-game schedule, it should be said) and had three seasons as somewhat of a contributor beyond it as well.
So I think we're talking about different things here. I don't think it's hard at all to conclude that Dunderdale had a lot more meat on the bone when full prime and full career are looked at. I'm baffled by the idea that one would come to the inverse conclusion looking at these stats. If you're saying Roberts achieved his feats consecutively, sure, I guess, but does that matter much?