I haven't actually played them seriously, but I'll try to analyze them based on what I see on the inspector and my experience playing Kailasa recently (but it wasn't in a really competitive game, though; I didn't need SCs for example).
Bandar Log's sacred recruitable troops are a 26g/17r monkey and a 70g/17r tiger rider with 10 hp and no trample or lance, versus Kailasa's 35g/5r 40-range archers (and assorted melee sacreds with essentially no protection). I think the archers are far, far better. There are a variety of things you can do with a bless - give them air shield (or you can just expect to use magic for it later), or quickness (again, spells), or regen, or boost their range, or take a rainbow pretender (this is what I did, but also boosted their range). They get especially deadly when you give them wind guide, and have gurus who buff them with etherealness and luck so that enemy armies that get close to them have a hard time even hitting them (and if your gurus can soul slay and enslave mind).
BL cannot acquire those archers at all - they have to make do with their 40 range ape archers, without any blesses. However, if they go with the light bandar archer, that's cheaper, at 18g/7r. (They don't dance either. (Celestial Music))
BL has the advantage of having troops that actually have decent amounts of protection. You actually need resources to recruit them, of course. With Kailasa I used production as my dump stat because resources weren't all that important except for recruiting indie troops, and my armies consisted mostly of archers, troops with some protection to get in the way of the enemy troops, and later a bunch of gurus. Also mercenary armies, because I had all of the gold ever.
Kailasa has recruitable 3E1N1H +WESN (+10% WESN), and 3W1N1H +WESN (+10% WESN) casters, which are very useful both for site-searching, crafting, and potentially for buffing or summoning. They cost 350 gold and are cap only, but only take one turn to recruit, and you know you'll get 3E1N or 3W1N when you recruit one. You can use the water ones to craft a bunch of clams of pearls for your gurus to power pearl-hungry combat spells like Power of the Spheres (which I combined with a Banner of the Northern Stars crafted by my pretender).
Bandar Log has recruitable monkey casters, who only have 1S, 2S1N, or 3S2N +WESN (+10% WESN). Their rishis - the ones with the random paths - cost 320 gold and are cap only and STR. So you don't know if you're going to get what you want, and you have to wait 2 turns to find out. If you want the 3E or 3W casters, you can summon them, and you need a 2N1E or 2N1W caster and 25 nature gems (in either case) to do it. So you have a 25% (or slightly more) chance each time you recruit a rishi to get the paths you need to be able to start burning 25 gems each to get the casters you actually wanted to have.
Besides the monkeys, their other casters are all summonable.
I mentioned these already:
2N1E and 25 nature gems for the Yaksha (3E1N1?)
2N1W and 25 nature gems for the Yakshini (3W1N1?)
The naga casters appear to require your pretender to summon, as not even the other summonable mages appear to have the needed paths:
They require 2W1E, 2W2E, or 3W3E and 25, 30, or 40 water gems. Kailasa lacked these casters, of course. Summoning even the cheapest one is impossible for a rishi unless it luckily gets both +W+E and then is given a water booster.
Potentially a lucky Nagini (2W1E+WESN) with a water and earth booster could get the 3W3E necessary to summon a Nagarishi, but considering that you only have a 25% chance to get the +1E you need per Nagini you summon, and they cost 25 gems each and then you would be making boosters, when the nagarishi only costs 40 and also comes with 3W3E+WESN(+10% WESN), you might be better off just using a rainbow pretender with 3W3E instead if you want to summon them.
(For the boosters the Nagini would need, either they'd need a blood stone, since they lack feet in naga form and lose 1W in their polymorphed with-feet form, or a robe of the sea, water bracelet, and earth boots in their polymorphed form)
BL may have an advantage when it comes to summoning the commanders which require astral, since their rishis can do it significantly easier than gurus:
Kinnaras, at 3S, which any rishi can summon. They're sacred flying commanders with 2A2S2H. I never used them, though.
Siddhas, at 4S, which 25% of rishis or any rishi with a starshine skullcap can summon. They're sacred teleporting commanders with 2A3S3H, who are excellent for throne-claiming and divine blessing sacreds, if you have any sacreds worth blessing. These guys have 4 hands and are ambidextrous.
Devatas, at 5S, which 25% of rishis with a starshine skullcap can summon. These guys are supposed to be badass 4-handed ambidextrous deathmurderers. I never bothered to summon any of them as Kailasa since nobody was fielding SCs. They'd probably be a hilariously effective SC or anti-SC with the right equipment. (Imagine equipping both vine shield and eye shield as well as actual weapons! Hohoho.)
There are also blood summons. There's nothing wrong with a nation having blood summons but their mages lacking the paths for it, as far as I'm concerned.
Overall they don't look quite as bad as I thought they would. I'd probably need to actually give them a try to see how it works out. The biggest problems I'm anticipating so far might be getting started early (as far as being able to knock over neighboring indies), early site-searching diversity, and getting enough gems to actually summon the casters you want to use.