transtemporal
Explorer
I'd tweak the monsters instead. If they're not challenging enough as written, make them more challenging. Increase their Dexterity, maximize their HP, give them a natural AC bonus or maybe use guerilla/spell-boosted tactics of their own. There's a lot you can do without significantly boosting the CR level. Or if they are over-powered for their level, throw them against encounters abover their level. I generally figure a 60%-65%chance of survival is a good norm for encounters. You may have to guess/estimate for a bit, but you will quickly zero in on what challenges your players.
What zardnaar is really saying is that an optimized parties
ability to output damage is probably broken because of the
sharpshooter and polearm master feats. Inflating monster stats and hp to address the problem
leads to grotesque solutions like CR 1/2 orcs with 50hp and 24str.