Looking for something equivalent to Sony 28-70
No such a lens in Canon world and the roadmap has nothing but big and heavy lenses, with the adapter the lenses feel heavier since they are farther from the body.
Actually my prefered lenses are Canon 28f2.8 and 50f1.8 but I want a zoom lens, 24-105 is fine but big and heavy, I am finding no decent compact and light standard zoom
Only adapting cheap EF zooms (from the film era) would help. Do you really want to go that route - put a rock bottom lens in front of a modern high resolution sensor? You're bound to be disappointed so why not just get the 24-105R and be done with it?
IMO, the RF 24-105L is the way to go, for now. AFAIAC, it is not really all that heavy, and optically it is very good indeed, way better than the EF variants. If you want something compact, I'd suggest the EF 40 F/2.8 with adapter. Slightly smaller, and lighter, than the RF 25 F/1.8 Macro, but works extremely well.
I have been looking at lenses for my R, but so far it looks like we have to be a little patient for now. The only alternative really is adapted lenses, especially in the range you are looking for. You could consider the EF 40 F/2.8 and/or EF 28 F/2.8 IS, or maybe even the 24 F/2.8 IS.
As to zoom lenses, you could go for the EF 28-135 STM, again, adapted. It is reasonably good.
HTH, kind regards, Wim
Gear: Canon EOS R with 3 primes and 1 zoom, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, 3 Metabones EF-MFT adapters, and a PhaseOne DF, P45+ back, SK 80 F/2.8 LS, 3 Mamiya lenses ...