If you really want to get all technical about it. Yes. In terms of training SB only, you'd get maybe 1 more pop on SB, but then we can go and say the extra sub levels you get on cross/secondary training also increases as well. We can also then say that it may be those sub levels that pop your ID/RB to the next level. So, will they be tangible pops? Maybe not, but if you were to include all the effects of a lvl 4 vs 5 trainer, yes you'd get about 1-2 extra pops in a season.
Personally when I hear 1-2 pops extra a season, I didn't think it'd be as drastic as training SB from 14 to 16 instead using a higher level trainer. I thought of it as, including the primary, and secondaries/cross training which sometimes can't be seen. Although I can see how the saying can be ambiguous