I honestly think you will find that ArcGIS Online is your best platform for sharing maps with co-workers. Since you specifically mentioned co-workers, I am assuming that what you want to publish and share shouldn't be publicly visible. If true, then you will find it difficult to beat the privacy of sharing the current GIS content you have to your organization constituents (I'm assuming they would be members of your ArcGIS organization). Especially since you mention ArcReader, which was a great product that leveraged your organization's data, you'll want to leverage that same content in a more modern web-based environment that ArcGIS Online provides.
And whether or not public access is your goal, the availability of easy-to-configure Instant Apps and app builders, Storymaps, and Dashboards just extends your capabilities, whether private or public. It would be very difficult for you to even come close to replicating that in some other platform especially if you want to keep things tightly coupled to your core assets.
As for "displaying the exact same way as in Pro" that should be doable, though you might need to think beyond Pro as the ultimate authoring environment and instead envision Pro as a way to create the building blocks that you will configure and assemble in ArcGIS Online. Map Viewer will likely not be your ultimate delivery vehicle to your intended audience, any of the configurable apps or app builders will likely be that vehicle.
I'd humbly suggest thinking beyond your previous ArcReader workflows and explore what is possible in today's online ecosystem. It will save you a lot of time and hassle, and be tightly coupled with your core GIS work.