Why is that? I've been doing bag work with 16s, but sparring with 18 oz gloves. Today was actually the first time I used 16s for sparring, and I didnt notice any difference.
Our old Ringside IMF Tech gloves were awesome, but someone I know ordered new ones recently and he had some quality issues with the padding they used. The damn things started clumping up, so he had to return them to get replaced.
You MUST become used to exertion in the gear you plan to go to war in. Why would you have multiple sized gloves unless you are pro and the glove you will use does not have enough protection for training? (Also consider pros are used to fighting so it doesn't matter what they train with.) The bag is for fitness and rough polishing. The mitts, shadow boxing, and sparring are for fine tuning. You would think you would want as much continuity between training aids/scenarios as possible. I would even tell anyone to gear up (head gear, cup, mouth piece, etc...) and work the bag occasionally, mitts, and do cardio with no less than a mouth piece. It only helps. I think that is the reason you see guys fidgeting with equipment in fights.
I have an old funky pair and still love them. I have to agree about current quality. I bought and returned two pair of them because the quality was cosmetically horrible. Wasted 32 bucks on S&H. Glad to know I made the right choice.
You fight in 10oz gloves not 16. Course it matters what pro's train with that's a ridiculous statement. The bottom idea is a good one though, like it.
I think we were both glossing over weight classes. If he is sparring in 16's, 16's on the bag would be fine (or maybe 14's). If he would use 10's in competition, as you suggested, he wouldn't be on the bag or sparring in more than 14's. Two gloves same size (sparring/training) are fine for both unless he is freakishly strong or brittle boned. Maybe for mitts he can pick up 12's if he has the cash to burn, but he doesn't. Why would it matter for a pro? They would choose what to use for protection. If they can use a 12? Fine. If they need an 18? Fine. If going from a 16/14/12 to a 10 throws you off at that level? You got other issues. Only way to go for cardio.
12oz for bagwork. Need that extra padding, but cutting off a few ounces will improve your power-endurance and keep you executing your techinques at high speed. Hell, we even used to spar in 12oz competition gloves. HUGE difference from 16's. Easier to slip a shot through, so you can't rely on a shell for defense. And your hands are just much faster