MC is strong Oracle bait for IND. Getting it early let's you drop forges, trade for Mono (and whatever else) for another +25% letting you fly through wonders (if only for failure cash).
If not, well the

and

bonuses are great, but normally it is such an easy trade (once the Wonder is gone) and so limited for brokering; better to open the Philo bulb or gun CS in a lot of games.
Beelines are somewhat useful:
a. Machinery; China and NA can do well with this. The CKN has no real counter and if you can get here before the AI gets construction you should have an easy war to win. NA archery untis are, of course, insane. While I normally try for an early LB push if I'm going to abuse SB, this can be better with a strong setup.
c. Engineering. Okay the AI LOVES this one, but beelining here quick let's you rip apart the AI trebs, pike + xbows vs LBs + garbage. HRE is slightly better, but I actually think this shot is stronger with CHA leaders if you can swing trades/GGs for 7 XP siege out of the box (CRIII trebs before castles or knights are insanely strong).
d. Guilds. Okay knights suck; their counter comes before they exist and they are only strong if the AI lacks Fe. However, catas are insane and camel archers can be decent. With some strong luck out to around Emp you can pull off maybe one war of archers vs knights (or replacement), but with Justinian or Sal this can be a very solid beeline.
f. Optics/Astro. In isolation you need to either commit to a highly efficient economy until the AI finds you (lots of wonder whoring and most likely cottages) or you need to commtt to finding the AI. Even when you are aren't completely isolated, getting access to more AIs can often be the biggest multiplier in the game. It is completely acceptable to get the basic worker techs and then to gun optics.