Cessna 150 has almost no dihedral to the wings much less than Cessna 172 and significantly less than low wing Piper.

The 172's and Piper's I have flown don't fly along perfectly straight and stable by themselves. I once flew a Piper Cherokee 140 for about 40min with nothing but my feet to keep it straight. That was the closest, but it still took some correction to keep her from doing what she wanted.

I used my 150 for an example because it's mine and I know exactly what it does.

Typically you have to trade off dutch-roll against spiral instability - getting both good is difficult.
It is typical to select a stable, damped dutch roll and allow slight spiral instability as this is more comfortable and safer than an underdamped dutch roll.

Of course WW1 aircraft were designed before this consensus on desirable characteristics was reached, so modern light aircraft are not in all respects a good analogue. The need to trade one against the other is true though, so you should either see a tendancy to hunt laterally, or a tendancy to spiral dive. If neither occurs then there may be some problem with this portion of the FM.

I know modern aircraft arn't the best comparison, but they still fly under the same set of physics.

For a fighter you would want less stability. Less stability = more maneuverable.

One other thing to consider is that when you let go of the stick in the sim, it goes to a preset held position, instead of following the airflow like it wants too. Right now letting go of the stick is the same as holding some back pressure in a real aircraft.

Supposedly these fighters are tail heavy, but the way the controls work it prevents them from displaying one of the earliest signs of being tail heavy. As the weight is moved rearward the pitch stability is decreased.

It's starting to get tail heavy when you pitch the nose to a certain point, let go of the controls and the nose stays at that pitch attitude. Instead of seeking back to it's desired attitude and attack angle for the airspeed it is trimmed at.

It's getting really tail heavy when you pitch to a certain attitude, let go and the nose continues going that direction. You better be on your toes or you may get a bad case of pilot induced oscillation.

With the controls always centering, ending up with a little up elevator, these tendencies go unnoticed if they are modeled. Surely none were so tail heavy for the second scenario, but the first is likely as it adds more maneuverability.

Remember what was said about the Camel, that it has to be flown at all times. The others aren't mentioned as being so bad, but I bet they were no pussycats.

Actually it's very common among pilots transitioning from Cessna 150-172 to Cherokee 140-180 to mismanage the fuel. The main reason is that in most Cessnas fuel selector have position "both" where fuel accessed from both tanks at the same time. However, in Cherokee you have to alternate between left and right tank every so often. When pilot forgets to do so one wing become heavier due to excessive fuel load and airplane tend to roll towards that wing Even though I was learning to fly in Cherokee I had suffered from similar "instability" phenomena

I switched it about every 30min in that Piper. The GPS even pops up and reminds you to switch tanks.

The 150's have a cross over line between the tanks, even so they will get uneven during flight. Since it only holds 12 gallons per tank, it usually doesn't get off by more than 3 gallons. An 18lb difference 3ft apart makes no noticeable difference if there is any turbulence at all.

A small weight shift can make a noticeable difference though. One very still and smooth night a friend and I were flying my 150 and he would turn around and move his bag, which was maybe 10lbs from the front to the rear of the luggage compartment, about about 2-3ft and back again. With hands off the controls you could see the nose raise and lower as he moved that small amount of weight.
We were probably pushing the gross weight of 1600lbs, which is in the same weight range of these ww1 fighters. So you can see that they are pretty sensitive to weight change.

I do find landing more difficult since that last patch. The aircraft seem to want to stall and drop a wing much more than before.

The NP17 will roll left if under power and one is "hands off," a nice modelling of torque.

The take off runs seem shorter now, I wonder if that's part of it? My Se5 seems to romp into the air now no problem, more like the replica aircraft do on youtube

I have 0 hours real world flight experience so I can't say that its right or wrong, I just agree with the op that things do feel slightly different. I'm having to take landings very carefully now, prior to 1007 I could land any aircraft in the sim even on uneven ground.