Seems to me that you could leave off the condition and have a solid build-around. As is, the card looks too hard to pull off to be worth the effort of playing.

that sounds much more desirable

Narrow and costly. Compare Crucible of Fire.

Most tribal cards aim to be inherently useful with a bonus for playing the tribe (e. g. by being a creature themself (inherently an attacker or blocker) or giving a usable effect that gets better with the tribe (e. g. Compelling Deterrence)).

Outside of that you really need to go for broke. Ideally this was a Glorious Anthem for four mana that gave an additional +1/+1 and strength to your Knights.

Alternatively just +1/+1 and strngth at a really large discount (e. g. ?) would be more compelling.

Independent of that: Mixing a static pump effect with a counter granting mechanic is sub-par design. Maybe this could replace the static +N/+N with something that grants counters as well e. g. "When ~ ETBs put a +1/+1 counter on each creature you control" and then the strength thing as a continuous effect.

It needs some re balances. I'd still like to keep it stronger than an anthem, I think white could do +2/+2 w/o breaking into green?

Maybe you are right about the alternative though, because you can get it out earlier...

I suppose that it is sub-par design bcus it is a mix of two things in a not so satisfying/simple way? (pt boost and activated counters)

I like the idea of an enter trigger, and I would be happy to have it like that for a lower cost, that way it's a bit more unqiue than another anthem

do you like this, does it need some tweaks/fixes?