Electronic – 2 Layer Through Hole PCB

If you don't want the leads to protrude on the bottom side you essentially want to mount your TH components as SMDs. So I would suggest to use SMD pads, push the leads onto the pads, and solder them there.

For large/heavy components this might give a mechanical reliability problem: a round wire soldered at both sides (or soldered at the bottom only but with a component immediately at the top) can't easily rip the copper from the PCB, but a lead soldered to an SMD pad can!

PCB material is not optimized for conducting heat, so you might want to put lots of via's in the appropriate places to conduct the heat.

I read in your edit that you want to do this for trough-hole screw connector blocks. My gut feeling is that this will seriously impact the mechanical reliability. You could consider using those two-level connectors for screw terminals, which would free room so you could put your heatsink under only a part of your PCB, leaving the area of the screw terminal terminals to be soldered at the bottom.

Although vias 'can introduce parasitics', the important thing is the detail, how much extra inductance in a via compared to a length of trace?

Your idea has merit, but without a more detailed analysis of path lengths, stray inductance, stray capacitance, of both layouts, it would not be possible to declare a winner.

In addition to overall length of the feedback path (and here we dive into more detail), the capacitance on the -ve input pin is a key factor in feedback stability, usually more important than the total length. Your method has to have a track long enough to escape the package on the side, whereas a via to the other side could place Rf directly opposite the -ve input pin.

It's often not clear whether 'short track length' is being used to encourage low inductance end to end, low stray capacitance to ground, or low phase shift when viewed as a transmission line. C to ground is a killer, and that stray ground capacitance varies proportionally to the length of the track, but only very weakly as the width, shortening the track is much more effective than making it narrower.

It's interesting to note that the highest speed op-amps (GHz GBW and above) have a pair of output pins both bonded directly to the output pin on the chip, one on the 'output' side for the conventional output, and one next to the input pin, for direct connection to the feedback components. Take a look at the Analog Devices' AD8045 data sheet for instance