One fact of platform pedals (even with pins) is that there is a % grade maximum that can be ridden at a constant speed. (Ie, not having a head of steam from the previous downhill. You can quite simply calculate the grade where your weight on the pedal (including whatever force you can effectively pull on the handlebars) operating through the crank arms, gear ratio and wheel diameter exactly matches gravity's pull on you and the bike. Steeper and you go backwards.
With foot restraint, you can pull up and at the same time push down harder on the opposite downstroke. You can now ride up far steeper grades. And yes, at any given RPM, your power and cardiovascular levels skyrocket. But - you can now loaf uphill far slower, Yes, the muscular needs are high, but with slow motion, you can cap the cardio (and as a by-product, reap some awesome full body muscular strength, especially if you incorporate your arms and sway the bike as a slow motion "dance".
For the OP, this isn't something he will want to do a lot of but there might be a staircase height of steep climb near home he can do periodically; a little like lifting weights.
I know all about what I am talking about here, I've been going up hills on fix gears 45 years. I've both "gone for it" like you see in my avatar; taken at a 14% stretch of a two mile climb and me in a 42-17 gear and loafed in the same gear up Portland's Germantown Road. There's a quick pitch on Portland's Rose Garden/Zoo climb that's around 20%. A test of my toestrap quality. Poor straps that slip and I have to walk it.