Can one define "church" too broadly?
Sure. One can easily define it too narrowly.
Any church that names the name of Christ, proclaims His deity, and teaches the death and resurrection of Christ is "the Chruch." I may have varying grades of disagreements with individual churches regarding doctrine or practice, but I still must respect them as true churches which proclaim the gospel of Christ. Christ is preached by them all, and for that I must still rejoice (Phil. 1:15-18).
My own personal yardstick is adherence to the Creeds. If a church either adheres to the Creeds or at least to the substance of them, then they are part of the "the Church."
The term which better describes me is "ecumenical," not "universalist." I couldn't give two hoots about denominations. Most of my generation couldn't either.
Only once have I been so mad I could spit - that was when a guy, teaching impressionable high schoolers, said "Only in [his particular type of church] is there liberty to worship in Spirit and in Truth" - as though the Baptists, the Presbyterians, the Pentacostals, or the Orthodox don't worship in Spirit and in Truth.