My stock brakes were not the best either, but got best performance by making sure they were set at the rec'd distance from the rim. 3 mm(?), about the thickness of a penny. Seems really close but if the rims are true, no problem. Also if the rim is not straight, the brakes don't work well on an uneven surface. Alos make sure the rim is centered between the brakes/calipers. If ou're off to one side, it can affect the power.
Easily centered by turning the little screw on top of the caliper arm. Tension can be set by tuning the barel adjuster at teh top of the caliper (where the cable meets the caliper). Easy fix and no need to take to the LBS.
The chain? One problem can be the crosschaining you mention. If you're in the midring and all the way to the inside, you are better off going to the small ring and finding a cog more towards the center. Many don't realize that some of the gears are repeats on triples. A gear combo on the midring can be matched by finding the combo on the small ring so there is really no need to crosschain. Works more efficiently if you use all the gears front, mid and small.
Some dopey people think it's unmacho to use the small ring. Prety silly since, like I said, the small can be matched with the rear to equal the mid ring gear.
In your case, you were on the samal front ring and the samll in the back. YOu needed a bigger gear. SO you should have swithed to the middle ring, then a bigger cog in the rear.
It's all about finding a siliar gear inch on each ring. An example.
You were in the small ring (32) and small cog(25). this equals 72 gear inches (from my lil book of gears
) but you were crosschained!
You should have been in the middle ring(42) and a cog closer to the center of the cog (16). This equals 71 gear inches which is almost 72 like the combo above. The 1 gear inch difference, you will not feel hardly at all, but it will keep your chainline straight and less of a chance of throwing the chain.
When you learn how to properly swithc gears, then if it flies off, you need to set the limit screws. The LBS can set the screws all they want but if you don't switch properly, it won't help.
A good tip is to chain the rear to a gear near the center before switching. Thes are called "transition cogs". Lessens the risk of throwing the chain. And since you are switching to an easier or harder gear, shouldn't affect your pedal pressure or stroke too much.
Use all your rings on the triple for more efficient shifting and riding.