Long lead times are nothing new for an aircraft at the start of it's service. Tornado engines took over a year to build and ship for a long time. When you buy an aircraft you should keep long lead time spares for the next 10 years. Back in the 90s the RAF had some spares that were 30 years old and yes they had wasted money on certain items that were hardly used while other items became unexpected consumables. I'm sure the same is true of the navy and army.
The UK is already completely reliant on the USA for defence, there's no going back now. If we dared to buy Mirage or Saab there would be repercussions - the USA could simply start refusing to repair F35s until we changed our mind. The top end example of UK/USA reliance is AWE is run by a joint company with Lockheed Martin being the majority shareholder, according to the FT.