Actually, I am going to disagree there. For years I fished bass with a 6 weight, then bumped to mostly 8 weights, but for the last two years, most of my bass fly fishing has been done with a 10 weight of one form or another, and I found myself less tired after a day of throwing the big rod.
The reasoning, I believe, is that it is much easier to throw big wind resistant flies, or heavy streamers (or in OP's case, senkos) with the heavier line mass of a 10 (or, as I often did, overlining with an 11 weight) weight line. That meant less false casting, and the benefit of longer casts when blind fishing lakes off the bank.
I got into streamers and top water stuff - bigger than typical dainty flies, similar in size to what I throw on gear rods - and an 8 weight just doesn't cut the mustard on a lot of that stuff, not without over lining, or over-exerting the casts with that light of a rod.
I caught crappie and lots of smaller bass on the 10, and it wasn't any less fun than catching a bluegill on a 6 weight.
When you hook into a better fish, the 10 weight has way more pulling power to get the fish out of cover, or control their run.
I've been working on my casting a lot this last year, and have tried to get to a point where one, two false casts at the most are done before firing the cast out. The bigger lines accomplish this much better.
For tossing 2-4 inch flies, sure the 8 weight is fine. I've gravitated to bigger flies hunting for bigger bites - my average streamer was 4-6 inches, and I had a few that went to 10 inches.
If you're going to throw soft plastics on a fly rod, a 10 weight is a good rod to do it with. You could toss a 5 inch senko if Texas rigged on a 10 weight pretty easy.