Had it not embarked on the ruinous 2001 bus war, one wonders whether First wouldn't still have a decent operation in the Lothians?
Absolutely
First had an established set of corridors, Lothian had enough on their plate (still running Atlantans into the 21st century, quite late to invest in low floor buses), if First hadn't bet the farm in 2001 I doubt Lothian were eager to fight
And, if they'd kept an Edinburgh network then they'd not have had to throw the towel in in Dalkeith/ Musselburgh/ Livingston etc (even if they did eventually give up the rural Borders stuff)
It seemed a good network, the 44/86/129/C3/C55 etc were long established, there was really no need for them to risk everything like they did. An unforced error, as sports commentators would say
I was too young to witness deregulation, but I’ve often wondered about how the various SBG companies around Glasgow seemed to get it so wrong, and what Strathclyde Buses did right
Some UK cities saw the "out of town" firm win chunks of the urban network, or even be merged with them (lots of municipals became part of the same group as the rural firms), some places saw very minimal competition (Dundee), it's hard to know what a good benchmark is (maybe Aberdeen, where Northern had a long established "city" operation that exists alongside the ex-GRT routes?) but I'd consider the following
Eastern Scottish succeeded in Edinburgh for a long time because they were the only competitor to LRT (Fife/ Lowland/ Midland focused on their own patches, rather than muscling in on the big city), so there was one coordinated alternative to the incumbent
The new Eastern services wholly within the city complemented the existing longer distance ones, e.g. Brunstane passengers had the same "green buses" doing the local C3 into town (later C2) as ran the services from Wallyford etc so might have been more likely to recognise/trust them (same with the 86 to Corstorphine, alongside 'green' buses to West Lothian)
In contrast, Glasgow had a messy combination of SBG firms, overlappping, getting in each others way, a myriad of colours. There were some coordinated tickets but I don't remember any coordinated publicity for SBG services (other than things the PTE produced with all operators)
Eastern also had the 'luxury' of only one real competitor in Dalkeith/ Musselburgh etc. They didn't have to deal with dozens of independents chucking breadvans on their turf as we saw in Airdrie/ Greenock etc. So SBG firms in the west had enough problems defending their bread and butter operations, meaning less focus on fighting with Strathclyde in Glasgow
Whilst the initial Eastern network was mainly run by conventional buses on fairly conventional routes, the success of the CitySprinter C5 in penetrating schemes encouraged them to invest in more minibuses, getting into places the maroon Atlantans couldn't touch - the Central/ Clydeside/ Kelvin Leopards etc didn't offer anything that Strathclyde weren't - in fact, Strathclyde seemed the ones investing in minibuses (there was something about 'group' fares on some, maybe they saw taxis as bigger competitiion?)
I don't know the pre-86 network in Glasgow but one of my suspicions is that Edinburgh's network at the time made it easy for a competitor to provide an attractive alternative. For example, in Lochend there was the 34/35 to the Bridges or the 42/46 to the Mound (each every twelve or fifteen minutes?). Eastern arrived with their C5, giving one simple service along Princes Street every five minutes, much easier for knowing where to go for your bus home. Certain Edinburgh streets didn't have a great service to where passengers might have preferred (Easter Road had the 1/6, but that took passengers up the Royal Mile - a gap Eastern exploited with their C55 to Princes Street). Maybe the more compact grid meant that Strathclyde penetrated central Glasgow well enough so that there wasn't a gap in the market for competition
Even though Eastern are long gone, some of their innovatiions can still be seen (the 8 in Craigour is a link introduced by the C11, the 37 to Pennywell is a link introduced by the C11, the diverted 1 along London Road is because of the C55 I mentioned above etc). What evidence is there in Glasgow of anything that Central/ Clydeside/ Kelvin introduced? Nothing seems to have any legacy (just a handful of Lanarkshire - Glasgow services that existed before 1986)