A segue but why can’t part time work? Why can’t the Reserve be a realistic component of a portfolio career?
I'm not being facetious, but have you actually tried it?
I struggled on with a reserve commitment for years, with hindsight deeply regretted the valuable time and money I'd lost to a very ungrateful and unrewarding system. Pretty much everyone i know from the same background came to the same conclusion. Its not coincidence that reserve recruiting and retention is bad.
I think the fundamental problem is that a reserve career stream is general immiscible with civilian life - networking, residence, family, administration, working practices are on different sides of a fence. That is not the case between comparable civilian roles.
In terms of "portfolio", lets not beat about the bush and face up to the fact that service experience on a CV is these days often seen in a negative light, or at least as something alien and of meaningless or unrecognised value. Service experience, being rather specialised and unique, arguably does not contribute to overall civilain "career" in the same way that multiple civilian roles do.
A fundamental problem is that the MoD/government is not a flexible employer, and is not prepared to invest in the sort of T&C that would compensate for the negative aspects to an individual of dipping into periods of service employment. Essentially that is because the government is attempting to have an Army without paying for it.