I just gave my Minutemen and militarized Settlers ballistic weave army fatigues and sturdy/heavy combat armor (heavy is more rare) so they sit between 100-200 def. A few get ballistic weave fedoras for an extra 110 def. There is no power armor necessary, as that much defense seems to last through through any conceivable fight...considering the weapons I give them... soupled up plasma/laser sniper rifles and gauss guns (take 1-3 hits to destroy a knight). Of course, the real kicker is rocket turrets that pretty much level any scene in seconds with a few heavy laser spaced in for variety.
I rarely bother with more than one power armor installation, but if you want them to use power armor, you need to provide it with a fusion core in a location that defenders will surely be (ie, near a guard post in a harder to reach area). Otherwise, enemies can get to the armor first. In combat, AIs will enter any available powered up power armor nearby. You want to be sure enemies don't take it.
It's pretty easy to build a force as the playergod that can best the BoS. You don't even have to get all that fancy as you'll have the benefit of turrets, which are quite formidable on the high end (rocket and heavy laser).
Of course, when people call the Minutemen weak, they generally exclude player influence, picturing the standard Minutemen patrols that have 30 def or so worth of shoddy armor and a crank operated laser musket. I'd argue that you HAVE to take into account player influence, as the faction is led by the player and only exists because the player reforms and rebuilds it. It seems a bit unrealistic that one individual can single-handedly arm an entire faction... of course, not much in the game IS realistic, so I'd argue there is little reason to start bickering over realism. At the end of the day, the in-game power of the Minutemen can, if built right, vastly exceed any other faction. Sadly, we can't do the same for other factions. I wish we had plotlines to eventually seize control over the various factions and actually be able to direct them. The BoS could definitely use some decent leadership...
Of course, the best faction is still the Atom Cats, regardless of overall strength.