With it, basic balancers lose their point entirely.

Yeah, it's basically a shortcut to let players bypass the balancer-building mechanic if they don't enjoy it.

You can increase the ingredient cost in mod settings if you want to maintain some incentive to keep building vanilla balancers.

Is it possible to make a 3-element balancer that doesn't take up 4 tiles?
I mean, it’s not a huge issue, but if I see three occupied blocks, the fourth one ought to be free—not blocking me from placing something like a conveyor belt there, unless that’s how it’s supposed to be.

If by "3-element" you mean "3 total belt connections", then yes -- just create a straight line of three balancer parts and you can connect a total of 3 belts to it (one to each balancer part).

If you mean 3 inputs and 3 outputs, the situation is more complicated. In Factorio 2.1 the game's rules for mods that overlap belt parts changed, making it impossible to have more than one belt connection to a single balancer part.

In Factorio 2.0 this restriction doesn't apply, but BetterBeltBalancer enforces it by default anyway to avoid the creation of balancers that will break when the save file is upgraded to Factorio 2.1

If you're never going to upgrade to 2.1 you can disable this check in BetterBeltBalancer's mod settings -- just know that balancers you create with more than one belt connection per balancer part will cease to function when you update to a 2.1 build of Factorio.

I have a feature request open with the Factorio devs to enable the 2.0 behavior on 2.1 -- if the requested change is implemented in the base game, I can remove this constraint entirely.

I mean, if I place two units facing forward and one to the left at the end of that pair, I can't put a conveyor belt next to the leftmost or rightmost unit because it causes a blockage—but that’s not a problem.

And would you add an option to enable the requirement for the balancer to need power?

and the power consumption would be the same as that of standard balancers

P.S. Everything made using the "Electric Powered Belts" mod.

And belt and balancer,tunel from mats logistics

I think it would make more sense for a belt electrification mod to modify Better Belt Balancer than for Better Belt Balancer to try and guess what a belt electrification mod should do; it's really beyond the scope of what Better Belt Balancer does. Vanilla splitters/balancers don't use power.

There's some precedent for this; Power Belts Extended has two optional dependencies for other belt-modifying mods that it will electrify if installed.

As far as faster belt types added by Matt's Logistics, they should work fine with Better Belt Balancer -- BBB looks through all available belt types and uses the fastest one it can find for its internal balancer construction, so if you have a mod that adds faster belts BBB balancers should automatically speed up to match.