As a high-sec industrialist, specialising in T2 invention, manufacture and sale then, yes, it is perfectly reasonable. A reasonably casual 1bn per month is possible. The interest is in understanding the supply/production chain and optimising that puzzle box as you see fit.
Yes, moving to null (and away from the markets!) could be more profitable, but I can’t be bothered with the hassles of the membership of some of those alliances.
Ultimately, the “is it viable” question is really “does it do give you what you want?” - it’s viable for me as in “it is financially self sustainable: ISK in is more than ISK I need” (I pay for Omega status, I’m not going to grind for ISK - Eve is fun, not a job).
What it does give me is the freedom to go “I’d like to try (X) content, Abyssal sites, fighting off Triglavian invasions, Mission ships and so forth” - while gently tending to my manufacturing works when I feel like. Just manufacturing and making ISK pales after a while, Eve has variety as well - it’s not all just sociopathic “go kill other players” as some may tell you.
Basically: It does work for me.