There is no issue having a vibration with the engine at low revs if it ticks over as the revs rise. The problems start when the engine is at high revs and there are still vibrations coming from the engine.
That's plain wrong. Not recognizing difference between vibration and oscillation as well. The oscillation issues at the beginning of 2017 and around the spec 3 of 2018 was due to torque cliff in low rev range and unstable/erratic combustion at low-mid rev range. The more you pursue lean burn, the more difficult it gets to control combustion in lower rev. Of course that's over whole range so same for high rev but in high rev it's easy to control by adjusting ignition timing etc to avoid knocking. This un-smooth, un-linear power delivery in lower rev was sending vibration and causing oscillation with interaction with gearbox, shaft, tyre and ground, that's why the counter measures they took was 1.avoid use of certain rpm in low-mid range, 2.shift down/up at non optimal timing to avoid the cliff spot, then 3.modify plenum chamber to improve low rev torque. That was up til Spain of 2017. For spec 3 of 2018 it's roughly the same as well but quite different in seriousness, basically they could cope with it by making software adjustment on dyno quickly as well as some minor hardware modification. The other issues on spec 3 was nothing to do with vibration but was mainly due to having used up all the safety margin incorporated in 2018 engine architecture at design stage.