I am-was a "Hardcore WM" user and didn't have multitasking issues as much as you are explaining. At first we were limited to 64MB RAM, which doesn't sound like much but it worked. Though you had to tame yourself to pretty much close all Tasks, so there was no/few actual background tasks.

Then shortly thereafter we got the 128MB RAM models. Previous users had no problem. Newbies did. But the extra ram meant extra performance (the cpu & gpu didn't get much faster). And we realized we could actually multitask (though you needed to figure out which programs were memory hogs).

Though WM didn't really get much of a turn for better multitasking. At about this stage xda became more popular (started off just unlocking carrier restrictions and themes) and programs became more sophisticated. What used to require 3 or 4 apps now was rolled into one. So multitasking got a back seat and instead the ecoystem matured a little.

The next phase started with the Kaiser, or what I call HTC's break from being a second-grade Chinese supplier to an actual OEM. This was their flagship and they came out guns blazing. They combined gps with telephony and the regular pda....into one single (thick) package with a keyboard so it wasn't that impossible.

What followed was maturing of HTC itself.
We got somewhat faster cpu and gpu (despite dodgy driver and class action lawsuits). The RAM got bumped up to 256MB and the birth of TouchFLO (aka Sense UI). One thing that HTC kept stuffing up was the builds. XDA is littered with many developer made builds which actually looked better, worked faster, used less battery (de-bloat).

The Diamond was the first of these "super-smart-phones" where they were able to combine all the features from the Kaiser with the improvements into a slim design. The only problem is they skimped on the battery size. The Touch Pro was the Daimond with a QWERTY but they refined it so well.

In fact, when you look back, it is as if Apple took all the ideas from the TouchPRO and made the first-gen iPhone. The TouchPRO2 came out, but it was a disappointment because it didn't bring much/if anything over the TP and suddenly Apple's revolutionary iPhone was superior to the HTC-Heavytitle. Nokia was creating Maemo during this time, but I'm not sure to say if those Internet Tablets were superior, let alone on-par with HTC's devices.

HTC after losing to Apple's appeal, signed a contract with Google for the G1. It was actually a developer phone that got pushed to the public to gain market share. In fact, it had so many bugs that it put people off android. However, developer communities rejoiced as it was open source and had technologically advancements over WM6.1, it was to be the iOS competitor and to do it before Microsoft could finish creating WM7 (ie WPhone). This gap in the market; with Windows Mobiles limited capabilities, Microsoft's withdrawal to the drawing board, and the immaturity of Android...let Apple's new ecosystem gain market share fast!

HTC's deals with Google deepened, and they realized Android was the way forward as Microsoft gave no promises. So thus Android began maturing as it did from v1.0 to 1.5 and 1.6 to 2.0 ...but now competing oems became interested too.
To celebrate HTC's last Windows Mobile project, they threw all the resources they had. The latest and greatest was packed in the Leo. You know this as the HTC HD2. With a High Definition display (800 x 480) and an enormous screen size (4.3in) and the fastest processor (first gen QSD), also all the gizmos/sensors the iPhone had, it was a true beast in its time.

But even that was surpassed, none other than by HTC itself, as they created the first "end-user" Google phone. The Nexus One. Now HTC stood chin-to-chin against iPhone's 3GS with no reason to slow down.

...many nights later
Android has cannibalized the market. Adoption skyrocketted but profits grew slimmer, it became a war of specs and marketing. Samsung came, saw and conquered. Apple had true reason to worry, but so did HTC which is learning that they can't produce half-assed products and expect to sell. And they're only just realizing the importance of customer satisfaction to actually generate word of mouth and also bring back previous consumers.