The main use for a fast telezoom for me is environmental nature shots in shaded forest, the best solution I ever had for that was the m.Zuiko 75/1.8 (150mm-e), but it wasn't very flexible since it was a prime. The m.Zuiko 40-150/4 Pro offered the flexibility (and was the fastest AF telezoom I'd bought previously) and the size/weight, but had no TC compatibility and still was lacking a bit of lens speed in some situations.
What I acquired is an original 70-200L f2.8 IS USM with a touch of Schneideritis (outer edge element separation in glued lens elements) that does not impact IQ. This gives me a fast, TC-compatible lens ideal for use in lower light situations like shady forests, at the cost of a frankly lousy MFD (1.4m) and a bunch of weight (almost 1.5Kg). It's a very situational lens and likely will stay home much of the time, but it is a good lens to have available in case, especially at the incredibly low price I paid for it due to the Schneideritis. With a 1.4x TC on the R7, it's also got enough reach for airshow and limited birding use, so I will have to add a TC to the kit as well. The main reason I would not normally look at a lens like this is it simply costs too much for something that's very situational for me, so getting one at a steep discount addresses the main downside of the lens for me.
It will be interesting to work with this lens, as it is so different from my usual choices in this focal length range. It will definitely stay home a fair bit due to the weight, but when I do haul it, I do expect to get shots I'd otherwise miss due to lack of light.
It also brings out just how good the experience of adapting EF lenses has been so far on the R7. I've used fully coupled adapters on m43, F and E/FE mounts and always found significant downsides. m43 was just terrible AF, even with a faster body like an E-M1 series, plus big lens/little camera handling issues. On F mount the FTZ adapter worked seamlessly with the 70-300E, but was a little annoying with older lenses, and the physical design made handling suck (the newer FTZII addresses the handling issue by dropping the useless integrated tripod mount that caused the handling issues) and in Sony the integration of mechanical aperture lenses was pretty meh (plus there were only a few SSM/SAM lenses with decent AF), and going with an EF to E adapter resulted in inconsistent performance.
With the EF to RF adapter, the experience so far has been seamless, although I'm only using native Canon glass for coupled adaptation (my Tamron 90mm is uncoupled, being a Nikon lens on a mechanical F to EF adapter). Aside from being a little large, I've had zero issues using the EF-S 10-18 IS STM, the EF 50mm f1.8 STM or the EF 70-200L f2.8 IS USM on the R7 with the standard Adapter. It's worth also noting that Canon actually makes 4 different adapters. There's an inexpensive standard adapter, a Control Ring version which has an additional control ring to substitute for the control ring that's on the RF lenses and not on EF lenses, a filter version which accepts a filter holder (available with either a polarizer or variable ND) and a Speedbooster, marketed for the Super35 cine bodies but which works fine on the RF-S bodies as well. My recommendation is to get the Control Ring adapter unless you have some reason to want one of the others. I have the standard one and plan to add the Control Ring version to my kit later in the fall.