The loaf tastes good and looks like a boulder, the blade drags and it splits at the side instead of opening

Two separate problems and it is worth fixing them in order, because the second one is caused by the first.

The drag is the blade and the angle. A razor pulled through dough at ninety degrees is trying to part it, and wet dough is sticky enough to follow the blade instead. What you want is a shallow angle, close to thirty degrees to the surface: and one confident, fast stroke. At that angle you are cutting a flap rather than a trench, and it takes far less force.

Depth matters too: for an ear you want a cut about half a centimetre deep, not a scratch. Shallow scores are the most common cause of no ear at all.

The blowout at the side is the loaf finding its own weakest point, and that happens when your cut did not give it a better one. The dough expands hard in the first minutes; if the score is too shallow or dragged and closed up, the pressure goes wherever the crust is thinnest - usually low on the side where the dough met the banneton.

So the sequence to fix: deeper cut, lower angle, faster stroke. When the cut is doing its job, the loaf opens there because that is genuinely the easiest path, and the side tear stops happening on its own.

One practical note: a razor blade on a stick is the right tool, and it must be sharp and clean. A blade with dried dough on it drags no matter what your technique is.

You are already doing the biggest thing right and may not know it: cold dough from the fridge cuts far better than room temperature dough. If you ever score at room temperature and wonder why it is worse, that is why.

A few things that make the cut cleaner still:

Score the moment it comes out of the fridge, not after it has sat on the counter while the oven finishes heating. Ten minutes of warming makes a real difference to how the surface behaves.

A dusted surface cuts more cleanly than a bare wet one. A light dusting of flour before scoring, brushed off after if you do not want it visible.

Do not saw. One stroke. If you go back over a cut it drags and closes, and that is often what turns a good score into a ragged one.

Wet the blade if it is still sticking, a quick dip in water between loaves.

On steam, since it is connected to your result: without enough steam the crust sets too early, and a set crust cannot open however well you scored it. That produces exactly the boulder shape. If you are not baking covered, or in a Dutch oven, that is worth checking before you spend more weeks on angles: plenty of no-ear problems are steam problems wearing a scoring costume.

The part that surprises people: most scoring problems are shaping problems arriving late.

A score opens because the surface of the loaf is under tension and the cut releases it in one direction. If the shaping did not build a taut skin, there is nothing to release, and the blade is just making a mark on a slack surface. That loaf will bulge and tear wherever it likes no matter how well you cut it.

How to tell which you have: after final shaping, the loaf should feel drum-tight on top and hold a domed shape rather than spreading. If it slumps in the banneton and comes out flatter than it went in, the tension is not there and the score cannot work.

The other thing shaping decides is where the weak point is. A seam that is not sealed properly underneath is a ready-made blowout, and it is usually low on the side: which is exactly where yours is bursting. Worth checking your seam is properly closed before it goes into the banneton.

So the order I would work through it: seam sealed, shaping tight, then the deeper and lower-angle cut described above, then steam. Change one at a time and give each two bakes, or you will not know which one did it.

And for what it is worth: a good crumb and good flavour means the hard parts are already working. This is the cosmetic end, and it is the most fixable.